drm/i915: WaEnableForceRestoreInCtxtDescForVCS is for video engines only

Also check for correct revision id in each Gen9 platform (SKL until B0
and BXT until A0).

Cc: Nick Hoath <nicholas.hoath@intel.com>
Signed-off-by: Michel Thierry <michel.thierry@intel.com>
Reviewed-by: Arun Siluvery <arun.siluvery@linux.intel.com>
Tested-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_lrc.c

@@ -301,10 +301,10 @@ uint64_t intel_lr_context_descriptor(struct intel_context *ctx,
 	/* desc |= GEN8_CTX_FORCE_RESTORE; */
 
 	/* WaEnableForceRestoreInCtxtDescForVCS:skl */
-	if (IS_GEN9(dev) &&
-	    INTEL_REVID(dev) <= SKL_REVID_B0 &&
-	    (ring->id == BCS || ring->id == VCS ||
-	    ring->id == VECS || ring->id == VCS2))
+	/* WaEnableForceRestoreInCtxtDescForVCS:bxt */
+	if (((IS_SKYLAKE(dev) && INTEL_REVID(dev) <= SKL_REVID_B0) ||
+	     (IS_BROXTON(dev) && INTEL_REVID(dev) == BXT_REVID_A0)) &&
+	    (ring->id == VCS || ring->id == VCS2))
 		desc |= GEN8_CTX_FORCE_RESTORE;
 
 	return desc;