Add multiboot 2 support to x86 bootloaders

multiboot 2 is required to boot Xen on an EFI system.
This also require a kernel patch for properly discovering
the ACPI RSDP, which is available after 20190912, in
src/sys/arch/x86/acpi/acpi_machdep.c 1.26-1.28

There are a few missing bit in this multiboot 2 implementation
(which are unused by Xen):
- Header tags Address, Freambuffer, and Relocatable are ignored
- Tags APM and Network are not provided
- Tags ACPI old and ACP new are only provided for ACPI boot
- Tag boot device does not provides the subpart (BSD disklabel partition)

Notes:
- multiboot2 is disabled in dosboot, otherwise the binary
gets too big and build fails.
- in src/sys/arch/i386/stand/efiboot, consinit() is renamed
as efi_consinit() to avoid prototype conflicts in src/sys/sys/systm.h

branches: 1.2.2; 1.2.6; 1.2.10; 1.2.16; 1.2.20; 1.2.24;
fix to be able to boot amd64 kernel from 32bit efiboot (booia32.efi).

branches: 1.1.2;
Initial commit of native amd64 EFI boot loader.

branches: 1.1.2; 1.1.4; 1.1.8; 1.1.18;
Initial commit of native amd64 EFI boot loader.

whitespace -> tab, blank line, no binary changes.

x86/efiboot: Nix trailing whitespace.

Add reloc keyworkd to let EFI bootstrap load amd64 kernel at any address

EFI bootstrap assumes it can copy the amd64 kernel to its ELF load
address (that is KERNTEXTOFF - KERNBASE = 0x200000), but it can
clash with previous UEFI memory allocation, as described here:
http://mail-index.netbsd.org/tech-kern/2023/04/07/msg028833.html

This change adds a reloc keyword for controling where the EFI
boostrap will copy the kernel image. Possible values are:
default - the default and prior behavior, copy at 0x200000.
none - do not copy and use the kernel image where it was loaded.
address - specify an explicit address where to copy the kernel.

This comes with an amd64 kernel patch that makes it self-relocatable.
It first discover where it was loaded in memory, and if this is
different than the expected 0x200000, hhe the kernel relocates
itself and start over at the right address.

branches: 1.5.26;
Add multiboot 2 support to x86 bootloaders

multiboot 2 is required to boot Xen on an EFI system.
This also require a kernel patch for properly discovering
the ACPI RSDP, which is available after 20190912, in
src/sys/arch/x86/acpi/acpi_machdep.c 1.26-1.28

There are a few missing bit in this multiboot 2 implementation
(which are unused by Xen):
- Header tags Address, Freambuffer, and Relocatable are ignored
- Tags APM and Network are not provided
- Tags ACPI old and ACP new are only provided for ACPI boot
- Tag boot device does not provides the subpart (BSD disklabel partition)

Notes:
- multiboot2 is disabled in dosboot, otherwise the binary
gets too big and build fails.
- in src/sys/arch/i386/stand/efiboot, consinit() is renamed
as efi_consinit() to avoid prototype conflicts in src/sys/sys/systm.h

branches: 1.4.2; 1.4.6;
efiboot: Added serial console support.

branches: 1.3.2; 1.3.8; 1.3.10;
efiboot: Boot parameters can be set via installboot(8).

branches: 1.2.2; 1.2.6; 1.2.8;
fix to be able to boot amd64 kernel from 32bit efiboot (booia32.efi).

branches: 1.1.2;
Initial commit of native amd64 EFI boot loader.

Avoid error with new binutils:
error: PHDR segment not covered by LOAD segment

branches: 1.1.2; 1.1.4; 1.1.8; 1.1.18; 1.1.20; 1.1.22;
Initial commit of native amd64 EFI boot loader.

branches: 1.2.8;
Fix multiboot32 argument usage

branches: 1.1.2; 1.1.4;
Add multiboot 2 support to x86 bootloaders

multiboot 2 is required to boot Xen on an EFI system.
This also require a kernel patch for properly discovering
the ACPI RSDP, which is available after 20190912, in
src/sys/arch/x86/acpi/acpi_machdep.c 1.26-1.28

There are a few missing bit in this multiboot 2 implementation
(which are unused by Xen):
- Header tags Address, Freambuffer, and Relocatable are ignored
- Tags APM and Network are not provided
- Tags ACPI old and ACP new are only provided for ACPI boot
- Tag boot device does not provides the subpart (BSD disklabel partition)

Notes:
- multiboot2 is disabled in dosboot, otherwise the binary
gets too big and build fails.
- in src/sys/arch/i386/stand/efiboot, consinit() is renamed
as efi_consinit() to avoid prototype conflicts in src/sys/sys/systm.h

branches: 1.2.8;
efiboot: Boot parameters can be set via installboot(8).

branches: 1.1.2; 1.1.4; 1.1.8; 1.1.10;
Initial commit of native amd64 EFI boot loader.

Add reloc keyworkd to let EFI bootstrap load amd64 kernel at any address

EFI bootstrap assumes it can copy the amd64 kernel to its ELF load
address (that is KERNTEXTOFF - KERNBASE = 0x200000), but it can
clash with previous UEFI memory allocation, as described here:
http://mail-index.netbsd.org/tech-kern/2023/04/07/msg028833.html

This change adds a reloc keyword for controling where the EFI
boostrap will copy the kernel image. Possible values are:
default - the default and prior behavior, copy at 0x200000.
none - do not copy and use the kernel image where it was loaded.
address - specify an explicit address where to copy the kernel.

This comes with an amd64 kernel patch that makes it self-relocatable.
It first discover where it was loaded in memory, and if this is
different than the expected 0x200000, hhe the kernel relocates
itself and start over at the right address.

branches: 1.2.2; 1.2.6; 1.2.14; 1.2.18; 1.2.26; 1.2.52;
efiboot: Don't access old stack after copying a kernel.

It's possible that the old stack is overwritten by the kernel.

fix to be able to boot amd64 kernel from 32bit efiboot (booia32.efi).