fbdev/cirrusfb: Add support for "64 MiB" version of Picasso IV

Some Village Tronic Picasso IV graphics cards identify as a 64 MiB Zorro
device in Zorro III mode.

While the total graphics memory size is the same on such cards, the offset
of the graphics memory differs. Add a quirk to handle this.

Based on src/sys/arch/amiga/dev/grf_cl.c from NetBSD.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Jeff Garzik <jgarzik@redhat.com>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>