drm/i915: s/PIPE_FRMCOUNT_GM45/PIPE_FRMCOUNT_G4X/ etc.

The PIPE_FRMCOUNT_GM45 and PIPE_FLIPCOUNT_GM45 names have bothered me
for a long time. The work equally well for ELK and onwards, so let's
s/GM45/G4X/.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>