vaapisink: rank it as secondary
vaapisink: rank it as secondary

iHD doesn't provide a full implemention for rendering surfaces and
i965 has problems in wayland. And I suspect this path is followed
by other driver implementations.

This patch demotes the rank of vaapisink to secondary, so it will
not be autoplugged avoiding bad experience of users.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer-vaapi/-/merge_requests/336>

GStreamer/gstreamer-vaapi,ceyusa/gstreamer-vaapi,GStreamer/gstreamer-vaapi,ceyusa/gstreamer-vaapi