st/vdpau: Provide YV12 to NV12 putBits conversion v2

st/vdpau: Provide YV12 to NV12 putBits conversion v2

mplayer likes putting YV12 data, and if there is a buffer format mismatch,
the vdpau state tracker would try to reallocate the video surface as an
YV12 surface. A virtual driver doesn't like reallocating and doesn't like YV12
surfaces, so if we can't support YV12, try an YV12 to NV12 conversion
instead.

Also advertize that we actually can do the getBits and putBits conversion.

v2: A previous version of this patch prioritized conversion before
reallocating. This has been changed to prioritize reallocating in this version.

Cc: Christian König <christian.koenig@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>