Bug#881358: breaks compatibility with libva1

[Jamon Terrell]

Not all applications have been updated to work with libva2, and debian
unstable does allow installation of libva1 and libva2 concurrently, but
this doesn't work for vdpau because vdpau-va-driver 0.7.4-6 only works with
libva1 and vdpau-va-driver 0.7.4-7 only works with libva2.  This forces
users who want libva1 support to manually install the older version of
vdpau-va-driver, and doesn't allow concurrent use of both.