video: Add support for non-BT.709 primaries

This add support for reading primary information from lavc, categorized
into BT.601-525, BT.601-625, BT.709 and BT.2020; and passes it on to the
vo. In vo_opengl, we always generate the 3dlut against the wider BT.2020
and transform our source into this colorspace in the shader.
options: Expose --primaries to the user
video: Support BT.2020 constant luminance system