Fix silent bus error panic on 98543A topcat framebuffer on HP320 and HP360.

It looks DELAY(100)s before checking cmap_busy in old pre-wscons grf_tc.c
http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/arch/hp300/dev/Attic/grf_tc.c?rev=1.42
are actually necessary on 68020 (HP320) and 68030 (HP360) machines,
while it works without them on 68040 (HP380).

Should be pulled up to netbsd-9.

(tsutsui)