The graphics domains are listed as GRDOM in the documentation, and the
GDRST PCI config register (0xc0) is only valid on I965 and GM45.  Newer
chips (like Sandy Bridge) have a different GDRST.
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>