lavc/videotoolboxenc: add hdr10, linear, hlg color transfer function for videotoolboxenc

lavc/videotoolboxenc: add hdr10, linear, hlg color transfer function for videotoolboxenc

Below is the testing ffmpeg command for the setting:
./ffmpeg -i input.ts -c:v hevc_videotoolbox -color_primaries bt2020 -colorspace bt2020_ncl -color_trc smpte2084 smpte2048.ts
./ffmpeg -i input.ts -c:v hevc_videotoolbox -color_primaries bt2020 -colorspace bt2020_ncl -color_trc linear linear.ts
./ffmpeg -i input.ts -c:v hevc_videotoolbox -color_primaries bt2020 -colorspace bt2020_ncl -color_trc arib-std-b67 hlg.ts

Signed-off-by: Limin Wang <lance.lmwang@gmail.com>
Signed-off-by: Rick Kern <kernrj@gmail.com>