vaapivideomemory: always prefer native VA surface formats.

vaapivideomemory: always prefer native VA surface formats.

Make sure to always prefer native internal formats for the VA surfaces
that get allocated. Also disable "direct-rendering" mode in this case.

This is needed so that to make sure that anything that gets out of the
decoder, or anything that gets into the encoder, is in native format
for the hardware, and thus the driver doesn't need to perform implicit
conversions in there. Interop with SW elements is still available with
fast implementations of VA imaging APIs.