sna: Periodically reduce the gpu damage (after migrating any cpu damage)

This will prevent the gpu damage list from growing unbounded.

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

src/sna/sna_accel.c

@@ -773,6 +773,7 @@ sna_pixmap_move_to_gpu(PixmapPtr pixmap)
 	priv->cpu_damage = NULL;
 
 done:
+	sna_damage_reduce(&priv->gpu_damage);
 	list_del(&priv->list);
 	return priv;
 }