v2: Actually implement interop between the gallium
    state tracker and the VDPAU backend.

v3: Make it also available in non legacy contexts,
    fix video buffer sharing.

v4: deny interop if we don't have the same screen object

v5: rebased on upstream changes

v6: implemented VDPAUGetSurfaceivNV, improved error handling,
    unregister all surfaces in VDPAUFiniNV

v7: squash merge with Mareks changes

Signed-off-by: Christian König <christian.koenig@amd.com>