move PRI_GUID, ARG_GUID, AVCodecGuid, ff_codec_guid_get_id, MEDIASUBTYPE_BASE_GUID and audio_guids[] to riff.c/h (add FF_ prefix to PRI_GUID, ARG_GUID, and MEDIASUBTYPE_BASE_GUID; rename audio_guids to ff_codec_wav_guids)
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>