Add check-vdpau helper
With this helper we are able to test if VDPAU is available and usable.
It is a simple test that renders a 4x4 surface and checks that the output is what we expected. (similar to the libvdpau-va-gl tests) Exit code is 0 on success.
As part of https://phabricator.collabora.com/T12900, this helper will be useful to test if a pressure-vessel container has all the correct bits that VDPAU requires. Also in the future we might even use this helper to show an additional entry in the s-r-s-i output.
/cc @smcv @jpwhiting
Edited by Ludovico de Nittis