Implement workaround for IBM405 Errata 77 (aka CPU_210), where
interrupted stwcx. may errantly write data to memory:

https://elinux.org/images/1/1d/Ppc405gp-errata.pdf

This is because stwcx. is split into two pieces in the pipeline.

We need to
(1) insert dcbt before every stwcx. instruction, as well as
(2) insert sync before every rfi/rfci instruction.

It is unclear which processors are affected, but according to Linux,
all 405-based cores up until 405GPR and 405EP are affected:

https://github.com/torvalds/linux/blob/master/arch/powerpc/platforms/40x/Kconfig#L140

For kernel, this workaround can be restricted to affected processors.
However, for kernel modules and userland, we have to enable it for all
32bit powerpc archs in order to share common binaries as before.

Proposed on port-powerpc:

http://mail-index.netbsd.org/port-powerpc/2020/02/21/msg003583.html

branches: 1.8.54; 1.8.58;
Add support pci_intr_setattr.
Export non-inline version of pci api for modules (_MODULE is defined).
Fix definition of pc_conf_hook and pc_conf_interrupt.
Switch to using inlines instead of macros.
Switch ibm4xx to use <powerpc/pci_machdep.h>

Change IBM4xx to use the common powerpc PIC framework.
Consolidate most ibm4xx initppc function into ibm4xx_init
and Make all IBM4xx use it.
Change explora to use initppc instead of bootstrap.

branches: 1.6.110;
merge ktrace-lwp.

include "conf/std".

branches: 1.4.16;
Remove SPILLSTK leftovers.

branches: 1.3.2;
Re-arrange things in evbppc & powerpc to support OEA-based eval boards
in evbppc. OEA-based board(s) to be added later.

Perform a rototill of the powerpc code. Mandate use of SPRG0 to store
a pointer to current cpu's cpu_info structure. Use cpu_info for
intstk,intr_depth,still_stk,idle_pcb,curpcb,curlwp,etal even on
non-MULTIPROCESSOR machines. Add common macros GET_CPUINFO and
INIT_CPUINFO to get and initialize the cpu_info struct on startup. Make
ibm4xx use the standard <powerpc/frame.h>. Use IFRAME_xx in ibm4xx
trap_subr.S instead of explicit magic offsets. Move INTSTK and SPILLSTK
to std.<platform>. Change faultbuf to a struct instead of an array.

On MPC6XX cpus, stop using the vector page for temporary space and use
reserved space in cpu_info.

branches: 1.1.2;
New umbrella-port for PowerPC-based evaluation boards.

The first board to be included here is the port to the 405GP-based
Walnut evaluation board, which up until now lived in arch/walnut.

arch/walnut will go away soon, once all the remaining walnut-isms
in the tree have been dealt with.