valkyriefb: various fixes

Valkyriefb and macfb will adopt the same card if they get the chance, so
remove valkyrie support from macfb. Also fix the "valkyriefb: can't do
832x624x8" problem reported by Raylynn Knight some time ago, by adding
vmode 13 support for CONFIG_MAC. Also add vmode 11 since that works too.
Make use of the monitor sense lines on 68k Macs too. Also some cleanups.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>