drm/i915/cnl: Add WaRsDisableCoarsePowerGating

Old Wa added now forever on CNL all steppings.

With CPU P states enabled along with RC6, dispatcher
hangs can happen.

Cc: Rafael Antognolli <rafael.antognolli@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180222200535.9290-1-rodrigo.vivi@intel.com

drivers/gpu/drm/i915/intel_guc.c

@@ -370,7 +370,7 @@ int intel_guc_sample_forcewake(struct intel_guc *guc)
 	u32 action[2];
 
 	action[0] = INTEL_GUC_ACTION_SAMPLE_FORCEWAKE;
-	/* WaRsDisableCoarsePowerGating:skl,bxt */
+	/* WaRsDisableCoarsePowerGating:skl,cnl */
 	if (!HAS_RC6(dev_priv) || NEEDS_WaRsDisableCoarsePowerGating(dev_priv))
 		action[1] = 0;
 	else