drm/i915: Ensure the HiZ RAW Stall Optimization is on for Cherryview.
This is an important optimization for avoiding read-after-write (RAW)
stalls in the HiZ buffer. Certain workloads would run very slowly with
HiZ enabled, but run much faster with the "hiz=false" driconf option.
With this patch, they run at full speed even with HiZ.
Increases performance in OglVSInstancing by about 2.7x on Braswell.
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>