drm/ttm: add ttm_bo_pipeline_gutting

Allows us to gut a BO of it's backing store when the driver says that it
isn't needed any more.

Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Roger He <Hongbo.He@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

include/drm/ttm/ttm_bo_driver.h

@@ -849,6 +849,15 @@ int ttm_bo_pipeline_move(struct ttm_buffer_object *bo,
 			 struct dma_fence *fence, bool evict,
 			 struct ttm_mem_reg *new_mem);
 
+/**
+ * ttm_bo_pipeline_gutting.
+ *
+ * @bo: A pointer to a struct ttm_buffer_object.
+ *
+ * Pipelined gutting a BO of it's backing store.
+ */
+int ttm_bo_pipeline_gutting(struct ttm_buffer_object *bo);
+
 /**
  * ttm_io_prot
  *