avformat: Avoid allocation for AVStreamInternal

Do this by allocating AVStream together with the data that is
currently in AVStreamInternal; or rather: Put AVStream at the
beginning of a new structure called FFStream (which encompasses
more than just the internal fields and is a proper context in its own
right, hence the name) and remove AVStreamInternal altogether.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavformat/nuv.c

@@ -133,7 +133,7 @@ static int get_codec_data(AVFormatContext *s, AVIOContext *pb, AVStream *vst,
                 }
                 ast->codecpar->codec_id = id;
 
-                ast->internal->need_parsing = AVSTREAM_PARSE_FULL;
+                ffstream(ast)->need_parsing = AVSTREAM_PARSE_FULL;
             } else
                 avio_skip(pb, 4 * 4);