etc.hp300, etc.sparc64: fix MKUPDATE handling

UPDATE was replaced with MKUPDATE 20 years ago,
but these directories were missed in the conversion.

Convert all the etc/etc.*/Makefile.inc to use RELEASEDIR/RELEASEMACHINEDIR
just like etc/Makefile does.

branches: 1.20.4; 1.20.10; 1.20.12; 1.20.14;
Add a comment reminding to update the release notes if the list of
kernels change.

Do ${MAKESUMS} for miniroot image.

Install release files under "${RELEASEDIR}/${MACHINE}/..." instead of
"${RELEASEDIR}/...".

${RELEASEDIR} is never cleaned , and ${RELEASEDIR}/${MACHINE} is only
cleaned if UPDATE is not defined.

- add snap_post, which makes "clean depend all release" in ../distrib/
for all platforms.
- remove now unnecessary replicated code in the various snap_md_post targets
- remove snap_md_pre; nothing uses it any more
- use ${NETBSDSRCDIR} and ${KERNSRCDIR} as appropriate

- consistency cleanup
- ensure INSTALLATION_DIRS contains the appropriate extra directories
for a given platform

Use INSTALLATION_DIRS for directory creation.

Make the install notes before trying to install them.

Drop into ${.CURDIR}/../distrib/${MACHINE} and make release.

Add a MAKESUMS variable which invokes makesums with CKSUM in its environment.
Use this whenever we want to invoke makesums.

EXTRA_KERNELS -> BUILD_KERNELS

Compile new installation kernel.

Change the way kernel sets are specified, and make them
more consistent. To quote the comment in etc/Makefile
that describes how it's done:

# This target builds the kernels specified by each port. A port may
# specify the following kernels:
#
# KERNEL_SETS The list of kernels that will be
# packaged into sets, named
# kern-${kernel}.tgz. These kernels
# are also placed in the binary/kernels
# area of the release package as
# netbsd-${kernel}.gz.
#
# EXTRA_KERNELS Additional kernels to place in the
# binary/kernels area of the release
# package as netbsd-${kernel}.gz, but
# which are not placed into sets. This
# allows a port to provide e.g. a netbootable
# installation kernel containing a ramdisk.
#
# BUILD_KERNELS Additional kernels to build which are
# not placed into sets nor into the
# binary/kernels area of the release
# package. These are typically kernels
# that are built for inclusion only in
# installation disk/CD-ROM/tape images.
#

Make sure to depend and build in hp300/stand before doing ``make release''.

branches: 1.7.2;
Build boot media and release notes under "snap_md_post", to complete
the "make release". Largely copied from the i386 port, and adapted.

branches: 1.6.2; 1.6.8;
Update all this crap so that `make snapshot' makes snapshots in release(7)
format, rather than in some unknown format. Also clean up the code a bit,
remove some code duplication, and add documentation to the Makefile.

Use "${MAKE}" instead of "make" for cross compilation.

These commits do two things:

1. Provide a consistent and extensible framework for compiling
kernels for the "make snapshot" target.

2. Add OBJDIR support for the "make snapshot" target, in the form
of three new make variables: KERNOBJDIR, KERNSRCDIR, and KERNCONFDIR.
Default values are in the Makefile.inc, and for OBJDIR they should
be defined in /etc/mk.conf as

KERNSRCDIR=${BSDSRCDIR}/sys
KERNOBJDIR=${BSDOBJDIR}/sys/arch/${MACHINE}/compile

The next step is to make a new target in the src/etc/Makefile for "release"
(or something like that) to make release(7) format files.

eliminate dangling references to config.old;
from Klaus Klein in PR misc/3295.

Overwrite existing snapshot kernel files when gzip'ing.

hp300-specific `etc' targets