gallium: move surface utility functions into u_surface.c

This is a better place than in u_rect.c

src/gallium/state_trackers/vega/renderer.c

@@ -40,6 +40,7 @@
 #include "util/u_memory.h"
 #include "util/u_rect.h"
 #include "util/u_sampler.h"
+#include "util/u_surface.h"
 
 #include "cso_cache/cso_context.h"