lavc/qsvdec: Add GPU-accelerated memory copy support

lavc/qsvdec: Add GPU-accelerated memory copy support

GPU copy enables or disables GPU accelerated copying between video
and system memory. This may lead to a notable performance improvement.
Memory must be sequent and aligned with 128x64.

CMD:
ffmpeg -init_hw_device qsv=hw -filter_hw_device hw -c:v h264_qsv
                    -gpu_copy on -i input.h264 -f null -
or:
ffmpeg -c:v h264_qsv -gpu_copy on -i input.h264 -f null -

Signed-off-by: Linjie Fu <linjie.fu@intel.com>
Signed-off-by: ChaoX A Liu <chaox.a.liu@intel.com>
Signed-off-by: Zhong Li <zhong.li@intel.com>