Pull up following revision(s) (requested by tsutsui in ticket #1627):

sys/arch/luna68k/luna68k/mainbus.c: revision 1.20

Fix device name for xpbus at mainbus for LUNA-II, missed on psgpam merge.

Fortunately harmless because xpbus_match() doesn't check ma_name in
mainbus_attach_args.

(martin)