i965: Mark upload buffers with MAP_ASYNC and MAP_PERSISTENT.

This should have no practical impact.  For the default uploader, we
don't really care, but for others, we may want to append more data
as the GPU is reading existing data, which means we need async and
persistent flags.

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

src/mesa/drivers/dri/i965/intel_upload.c

@@ -87,7 +87,9 @@ brw_upload_space(struct brw_uploader *upload,
    if (!upload->bo) {
       upload->bo = brw_bo_alloc(upload->bufmgr, "streamed data",
                                 MAX2(upload->default_size, size), 4096);
-      upload->map = brw_bo_map(NULL, upload->bo, MAP_READ | MAP_WRITE);
+      upload->map = brw_bo_map(NULL, upload->bo,
+                               MAP_READ | MAP_WRITE |
+                               MAP_PERSISTENT | MAP_ASYNC);
    }
 
    upload->next_offset = offset + size;