drm/i915/mtl: Disable C6 on MTL A0 for media

Earlier merge dropped an if block when applying the patch -
"drm/i915/mtl: Synchronize i915/BIOS on C6 enabling". Bring back the
if block as the check is required by - "drm/i915/mtl: Disable MC6 for MTL
A step" to disable C6 on media for A0 stepping.

Fixes: 37350409 ("drm/i915/mtl: Synchronize i915/BIOS on C6 enabling")
Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Reviewed-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230324213918.75212-1-umesh.nerlige.ramappa@intel.com

drivers/gpu/drm/i915/gt/intel_rc6.c

@@ -525,6 +525,13 @@ static bool rc6_supported(struct intel_rc6 *rc6)
 		return false;
 	}
 
+	if (IS_MTL_MEDIA_STEP(gt->i915, STEP_A0, STEP_B0) &&
+	    gt->type == GT_MEDIA) {
+		drm_notice(&i915->drm,
+			   "Media RC6 disabled on A step\n");
+		return false;
+	}
+
 	return true;
 }