drm/i915: Transform WaDisableDynamicCreditSharing into a simple register write

GAMT_CHKN_BIT_REG does not live in the context image.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
Reviewed-by: Michał Winiarski <michal.winiarski@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1504798809-5653-5-git-send-email-oscar.mateo@intel.com
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_engine_cs.c

@@ -1130,8 +1130,9 @@ static int kbl_init_workarounds(struct intel_engine_cs *engine)
 
 	/* WaDisableDynamicCreditSharing:kbl */
 	if (IS_KBL_REVID(dev_priv, 0, KBL_REVID_B0))
-		WA_SET_BIT(GAMT_CHKN_BIT_REG,
-			   GAMT_CHKN_DISABLE_DYNAMIC_CREDIT_SHARING);
+		I915_WRITE(GAMT_CHKN_BIT_REG,
+			   (I915_READ(GAMT_CHKN_BIT_REG) |
+			    GAMT_CHKN_DISABLE_DYNAMIC_CREDIT_SHARING));
 
 	/* WaDisableFenceDestinationToSLM:kbl (pre-prod) */
 	if (IS_KBL_REVID(dev_priv, KBL_REVID_A0, KBL_REVID_A0))