vda: use hwaccel private data for internal bitstream buffer
Merge commit '31a46750c7eafe6bce6a3e4f09853cd0a585292b'

* commit '31a46750c7eafe6bce6a3e4f09853cd0a585292b':
  vda: use hwaccel private data for internal bitstream buffer

Conflicts:
	libavcodec/vda.h
	libavcodec/vda_h264.c

Merged-by: Michael Niedermayer <michaelni@gmx.at>