Dolby Vision support (mp4/avformat parsing, OpenGL vout)

This patch-series implements additional support for Dolby Vision in VLC:

• Parsing/retrieving the stream-wide Dovi configuration records from the mp4 and avformat demuxers and add it as part of video_format_t.
• Forwarding this to the OpenGL filters
• (Provisionally) Conditionally enabling pl_scale when DoVi handling is required, even on the default upscaler/downscaler setting

This ultimately allows OpenGL to handle DoVi streams (including profile 5), sans EL, using more-or-less existing code paths.