avcommon: use a specific macro to check the FFmpeg libavformat version

avcommon: use a specific macro to check the FFmpeg libavformat version

This macro doesn't check for libav which is assumed to not have to relevant
code. This is the same macro name used in VLC 4.0.

Gbp-Pq: Name 0085-avcommon-use-a-specific-macro-to-check-the-FFmpeg-li.patch