drm/i915/icl: WaAllowUMDToModifyHalfSliceChicken7

Required to dinamically set 'Trilinear Filter Quality Mode'
Userpsace consumer is mesa.

V2: Rebase
V3: Update commit message

Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: NOscar Mateo <oscar.mateo@intel.com>
Signed-off-by: NRadhakrishna Sripada <radhakrishna.sripada@intel.com>
Reviewed-by: NAnusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: NRodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181030084504.21537-3-radhakrishna.sripada@intel.com

drivers/gpu/drm/i915/intel_workarounds.c

@@ -1016,6 +1016,8 @@ static void cnl_whitelist_build(struct whitelist *w)
 
 static void icl_whitelist_build(struct whitelist *w)
 {
+	/* WaAllowUMDToModifyHalfSliceChicken7:icl */
+	whitelist_reg(w, GEN9_HALF_SLICE_CHICKEN7);
 }
 
 static struct whitelist *whitelist_build(struct intel_engine_cs *engine,