vaapipostproc: HDR10 Tone Mapping

Adds support for HDR10 tone mapping.

#222

Example:

gst-launch-1.0 -vf filesrc location=HDR10-Video.webm \
 ! matroskademux ! vaapivp9dec \
 ! vaapipostproc hdr-tone-map=auto \
 ! "video/x-raw(memory:VASurface),format=P010_10LE,colorimetry=bt2020-10" \
 ! vaapisink fullscreen=1

gst-launch-1.0 -vf filesrc location=HDR10-Video.webm \
 ! matroskademux ! vaapivp9dec \
 ! vaapipostproc hdr-tone-map=auto \
 ! "video/x-raw(memory:VASurface),format=BGRA,colorimetry=sRGB" \
 ! vaapisink fullscreen=1

Tested on KBL