Merge commit '12ab667e'

* commit '12ab667e':
  matroska: use av_stream_add_side_data() for stereo3d side data
  mov: Use av_stream_add_side_data() for displaymatrix side data
  utils: Add av_stream_add_side_data()

This is a noop, see
2ab50647
77f033eb
2343f23eMerged-by: James Almer <jamrial@gmail.com>