drm/i915: Move the invalidate|flush information out of the device struct

... and into a local structure scoped for the single function in which
it is used.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

include/drm/drmP.h

@@ -1041,8 +1041,6 @@ struct drm_device {
 	/*@{ */
 	spinlock_t object_name_lock;
 	struct idr object_name_idr;
-	uint32_t invalidate_domains;    /* domains pending invalidation */
-	uint32_t flush_domains;         /* domains pending flush */
 	/*@} */
 
 };