egl-headless depends on the backing surface to be set before texture are
set and updated. Display it (update=true) iff the current scanout kind
is SURFACE.

Reported-by: Akihiko Odaki <akihiko.odaki@gmail.com>
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>