drm/i915: fully switch off overlay when not in use

Now that the cache flushing of the memory based overlay regs works,
we can safely switch off the overlay. Beforehand it was only disabled
(like in userspace).

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Eric Anholt <eric@anholt.net>
diff --git a/drivers/gpu/drm/i915/intel_overlay.c b/drivers/gpu/drm/i915/intel_overlay.c
index 3f6f3a3..4e88abb 100644
--- a/drivers/gpu/drm/i915/intel_overlay.c
+++ b/drivers/gpu/drm/i915/intel_overlay.c
@@ -323,7 +323,6 @@
 	}
 
 	/* turn overlay off */
-	/* this is not done in userspace!
 	BEGIN_LP_RING(6);
         OUT_RING(MI_FLUSH);
         OUT_RING(MI_NOOP);
@@ -338,7 +337,7 @@
 		DRM_ERROR("intel overlay: ring sync failed, hw likely wedged\n");
 		overlay->hw_wedged = 1;
 		return ret;
-	}*/
+	}
 
 	overlay->active = 0;