drm/xe: Only try to lock external BOs in VM bind

We only need to try to lock a BO if it's external as non-external BOs
share the dma-resv with the already locked VM. Trying to lock
non-external BOs caused an issue (list corruption) in an uncoming patch
which adds bulk LRU move. Since this code isn't needed, remove it.

v2: New commit message, s/mattthew/matthew/
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/xe/xe_vm.c

@@ -2157,9 +2157,11 @@ static int vm_bind_ioctl(struct xe_vm *vm, struct xe_vma *vma,
 		 */
 		xe_bo_get(vbo);
 
-		tv_bo.bo = &vbo->ttm;
-		tv_bo.num_shared = 1;
-		list_add(&tv_bo.head, &objs);
+		if (!vbo->vm) {
+			tv_bo.bo = &vbo->ttm;
+			tv_bo.num_shared = 1;
+			list_add(&tv_bo.head, &objs);
+		}
 	}
 
 again: