drm/i915: Implement Wa4x4STCOptimizationDisable:chv

Wa4x4STCOptimizationDisable got only implemented for BDW, but according
to the w/a database CHV needs it too, so add it.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Arun Siluvery <arun.siluvery@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>