libavcodec/qsvenc_av1: add av1_qsv encoder

It is available only when libvpl is enabled. MSDK doesn't support av1
encoding.

sample command:
ffmpeg -f rawvideo -pix_fmt nv12 -s 1920x1080 -i input.yuv \
-c:v av1_qsv output.ivf

Signed-off-by: Wenbin Chen <wenbin.chen@intel.com>
Signed-off-by: Haihao Xiang <haihao.xiang@intel.com>
