Fix bink audio playback outside of FFmpeg.

There are 2 known Bink audio codecs. Additionally they have
a different flavor if they are found inside Bink-b "BIKb" file.
In order to guess the correct flavor, the demuxer sets the audio
codec_tag to be the same as the file format tag.
This causes problem because same tag is used for both audio codecs.
The hack works in FFmpeg because audio codecs are identified by their
codec_id, but other players rely on standard behavior.

This fix removes the codec_tag hack and instead uses artificial
extradata format to signal the codec flavor. This would also
allow proper embedding of Bink audio in other containers.

Signed-off-by: Ivan Kalvachev <ikalvachev@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
