Direct commit to stable

Remove libstand32 here. pc98 is a 32-bit platform, so it shouldn't compile
the extra 32-bit copy of libsa. The copy built in libstand is already 32-bit.
Add a comment saying we need an empty Makefile.pc98 since otherwise it would
pull in Makefile.i386 and there is no EFI on pc98, and the machines are too
old to have ZFS or GELI be a viable option (and besides, those don't compile).

Note: We also need r331140 to be MFC'd for pc98 build to work in all cases.

MFC r325834,r325997,326502: Move sys/boot to stand/

This is effectively a direct commit to stable/11, due to differences between
stable/11 and head. Changes to DTS in sys/boot/fdt/dts were often
accompanied by kernel changes. Many of these were also risc-v updates that
likely had many more dependencies to MFC.

Because of this, sys/boot/fdt/dts remains as-is while everything else in
sys/boot relocates to stand/.

r325834: Move sys/boot to stand. Fix all references to new location

r325997: Remove empty directories.

r326502: Document the sys/boot -> stand move in hier.7 and the top-level README.