[Libva] [RFC] VA API extension proposals to support encode and post-processing

[Xiang, Haihao]

> Can we push the latest vaapi-ext changes? It seems the current fd.o tree does not contain the latest additions and this split to va_vpp.h.
> 
> >> Haihao, could you check if the latest version have been pushed to the fd.o repository on the vaapi-ext branch.

The latest version has been pushed, including new "flags" field to
VAProcInputParameterBuffer and data structures for JPEG decoding, all
interfaces are still in va.h

Thanks
Haihao