libvdpau updates

[Andreas Beckmann]

Hi Andres, hi Russ,

I just updated the vdpau package in the git repository.
Actually this was the first time I did some packaging with git, I hope I
didn't mess up too many things.

Major changes:
 switch to multiarch (and search in multiple directories)
 doc package build cleanup

Another fix (patch cherry picked from upstream) could possibly fix
#592204. Andres, please check again and convert the "This could fix
#592204" to a proper Closes: if the issue is no longer reproducible.

It would be nice if someone of you could upload the updated libvdpau
package.

There is also my ITP of vdpauinfo still pending: #631661


Andreas