[SCSI] advansys driver: limp along on x86

Let people enable the advansys driver on x86-32, even though it's broken
on other architectures due to missing DMA mapping infrastructure.

It's used by Jeffrey Phillips Freeman <jeffreyfreeman@syncleus.com> and
possibly others.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Adrian Bunk <bunk@stusta.de>