agp: add support for Radeon Mobility 9000 chipset

Addresses https://bugs.edge.launchpad.net/ubuntu/+source/linux-source-2.6.22/+bug/178634



Signed-off-by: Amit Kucheria <amit.kucheria@ubuntu.com>
Signed-off-by: maximilian attems <max@stro.at>
Acked-by: Dave Airlie <airlied@linux.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>