drm/radeon: let sa manager block for fences to wait for v2

Otherwise we can encounter out of memory situations under extreme load.

v2: add documentation for the new function

Signed-off-by: Christian König <deathsimple@vodafone.de>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon.h

@@ -362,7 +362,7 @@ struct radeon_bo_list {
  * alignment).
  */
 struct radeon_sa_manager {
-	spinlock_t		lock;
+	wait_queue_head_t	wq;
 	struct radeon_bo	*bo;
 	struct list_head	*hole;
 	struct list_head	flist[RADEON_NUM_RINGS];