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: <!336>
parent b387081a
Pipeline #173352 waiting for manual action with stages
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