mesa/st: mark internal buffer map call as UNSYNCHRONIZED

these are new buffers with empty contents which are immediately
unmapped after a memcpy, so there's no reason to force
the driver (or tc) to sync

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36634>

src/mesa/main/bufferobj.c

@@ -360,7 +360,9 @@ bufferobj_data(struct gl_context *ctx,
          obj->buffer = screen->resource_create(screen, &buffer);
 
          if (obj->buffer && data)
-            pipe_buffer_write(pipe, obj->buffer, 0, size, data);
+            pipe->buffer_subdata(pipe, obj->buffer,
+                                 PIPE_MAP_WRITE | PIPE_MAP_DISCARD_WHOLE_RESOURCE | PIPE_MAP_UNSYNCHRONIZED,
+                                 0, size, data);
       }
 
       if (!obj->buffer) {