This is a direct commit to stable/11 due to pc98 removal from head.
Several improvements in head that were MFC'd left the pc98 build broken in
stable/11. Massage the pc98 bits to get it to at least build.
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.
