lavc/hevc Parse SEI_TYPE_MASTERING_DISPLAY_INFO and propagate content into the AVMasteringDisplayMetadata side data.

Add support for parsing SEI_TYPE_MASTERING_DISPLAY_INFO and propagate contents into
the AVMasteringDisplayMetadata side data. Primaries are ordered in RGB order and
the values are converted to rationals ([0,1] for CEI 1931 Chroma coords,
and cd/m^2 for luma).
Signed-off-by: Neil Birkbeck <neil.birkbeck@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>