virgl/vtest-winsys: Use virgl version of bind flags

The bind flags defined by mesa/gallium might not always be in sync
with the ones copied to virglrenderer/gallium. Therefore, use the
flags defined in virgl like it is done for all the other calls to
create resources.

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
(cherry picked from commit b710680093a29d4f7dcde2e5a3ee61bba80404ca)