gxfb: move MSR bit fields into gxfb.h

This continues the gxfb header cleanups.  MSRs are defined in geode.h; the
specific bits we care about are defined in gxfb.h.

Signed-off-by: Andres Salomon <dilinger@debian.org>
Cc: Jordan Crouse <jordan.crouse@amd.com>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>