drm/amdgpu/ttm: handle tt moves properly.

The core move code currently handles use_tt moves, for amdgpu
this was being handled also in the driver, but not using the same
paths.

If moving between TT/SYSTEM (all the use_tt paths on amdgpu) use
the core move function.

Eventually the core will be flipped over to calling the driver.
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200924051845.397177-4-airlied@gmail.com

drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c

@@ -671,14 +671,16 @@ static int amdgpu_bo_move(struct ttm_buffer_object *bo, bool evict,
 		ttm_bo_move_null(bo, new_mem);
 		return 0;
 	}
-	if ((old_mem->mem_type == TTM_PL_TT &&
-	     new_mem->mem_type == TTM_PL_SYSTEM) ||
-	    (old_mem->mem_type == TTM_PL_SYSTEM &&
-	     new_mem->mem_type == TTM_PL_TT)) {
-		/* bind is enough */
+	if (old_mem->mem_type == TTM_PL_SYSTEM &&
+	    new_mem->mem_type == TTM_PL_TT) {
 		ttm_bo_move_null(bo, new_mem);
 		return 0;
 	}
+
+	if (old_mem->mem_type == TTM_PL_TT &&
+	    new_mem->mem_type == TTM_PL_SYSTEM)
+		return ttm_bo_move_ttm(bo, ctx, new_mem);
+
 	if (old_mem->mem_type == AMDGPU_PL_GDS ||
 	    old_mem->mem_type == AMDGPU_PL_GWS ||
 	    old_mem->mem_type == AMDGPU_PL_OA ||