drm/i915/gen9: Add WaSetDisablePixMaskCammingAndRhwoInCommonSliceChicken

In Indirect context w/a batch buffer,
+WaSetDisablePixMaskCammingAndRhwoInCommonSliceChicken

v2: SKL revision id was used for BXT, copy paste error found during
internal review (Bob Beckett).

v3: explain why part of the WA is in Per ctx batch (Mika)

Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Signed-off-by: Arun Siluvery <arun.siluvery@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>