Build install ramdisk kernel for JORNADA720.

Added Sharp W-ZERO3 series support.

Invoke ${MAKESUMS} for ${RELEASEDIR}/${RELEASEMACHINEDIR}/installation files
as snap_md_post target in etc/etc.${MACHINE}/Makefile.inc rather than
as release target in distrib/${MACHINE}/Makefile so that builds for
release in distrib/${MACHINE}/Makefile don't have to be serialized.

XXX: maybe ramdisk kernels should be installed into binary/kernel dir
XXX: as other ports rather than installation dir, and
XXX: kernel config names should be preserved in their filenames.

- add INSTALLATION_DIRS+=installation/miniroot so that miniroot.fs.gz
image is installed properly
- INSTALL_IPAQ should be in BUILD_KERNELS rather than KERNEL_SETS
since it requires ramdisk image by mdsetimage(8) in src/distrib

branches: 1.6.12; 1.6.18;
Add a comment reminding to update the release notes if the list of
kernels change.

branches: 1.5.4; 1.5.8;
Add INSTALL_IPAQ to build.

consistency tweaks

- 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

hpcarm isn't hpcmips.

Add a minimal set of etc.hpcarm/* files.