vapostproc: Process HDR caps fields
This patch adds a new parameter: hdr-tone-mapping (same as vaapipostproc). If HDR filter available in driver the parameter is expose, but it's disabled by default.
If hdr-tone-mapping is enabled then HDR fields in sink caps are filtered in frames, from HDR to SDR, removing those hdr fields in source pad caps too.
hdr-tone-mapping is not enabled if a color conversion is also requested, since it fails to process in the iHD driver, so far.