[PATCH oneiric] drm/i915: set GFX_MODE to pre-Ivybridge default value even on Ivybridge

[Robert Hooker]

This is a commit in 3.1 that fixes a frequent GPU hang on ivybridge
and is not yet in stable.
It adds a few new register defines, then uses them only on GEN7 which
is ivybridge so it does
not affect any other generation making it safe to apply. It is a clean
cherry-pick into oneiric and
was tested on an ivybridge machine.