sparc cg14, sx & mgx framebuffer changes

tl;dr - netbsd-10 builds with cg14, sx & mgx framebuffer improvements
in https://sync.absd.org/sparc/netbsd-10/ &
https://sync.absd.org/sparc64/netbsd-10/

I've just taken a pass through recent NetBSD HEAD changes for sparc
framebuffers, and generated a set of patches looking to get the
changes pulled up into netbsd-10 before (pretty much all of these are
by macallan@, my only input here is in running cvs diff & patch)

The changes primarily affect sparc cg14, sx & mgx framebuffers
- Glyphcache alignment to allow SX to use 32 bit  accesses as much as
possible, although there is other hardware where it would help as
well, for example permedia 2
- Changes to vcons to avoid framebuffer writes to help on slow framebuffers
- Initialise sx diagnostic register (yields a 10% speed increase when
rendering antialiased text)
- periodically drain the instruction queue in order to avoid stalling
the MBus on sx & cg14
- mgx improvements, including caching DEC & FG registers &  avoiding
waiting where possible

This is on top of existing changes from netbsd-9, which include many
small improvements and bugfixes, plus adding proper 8bit support to
the hw acceleration code in xf86-video-suncg14 for people with 4MB
cg14 who prefer higher resolutions over colour depth. (According to
x11perf it's somewhere between a turbo and a non-turbo GX, but one
that can do 1920x1200. And
a 4MB cg14 is probably easier to find than a TGX+)

Again, all I'm doing is testing patch pullups into a netbsd-10 tree,
with an eye to submitting them for the official release, and making
them available for anyone interested with hardware (and inviting
feedback :) Most of these changes will affect console usage, while
others X11.

I've put full release builds at
  https://sync.absd.org/sparc/netbsd-10/
and
  https://sync.absd.org/sparc64/netbsd-10/

(also available via http for those that swing that way)

The directories also include the sparc-cg14-sx-mgx.pullup &
sparc-cg14-sx-mgx.patch files which detail what has changed from a
standard netbsd-10 tree, for anyone who prefers to "./build.sh -x -U
-m sparc -j 6 release" themselves.

Thanks

David