Support audio playing (AT3, AT3+, Mp3, AAC)

After vrious disussion https://github.com/hrydgard/ppsspp/pull/5672 https://github.com/hrydgard/ppsspp/issues/5689 https://github.com/hrydgard/ppsspp/issues/5654  https://github.com/hrydgard/ppsspp/issues/5660 https://github.com/hrydgard/ppsspp/pull/5656  https://github.com/hrydgard/ppsspp/pull/5657  https://github.com/hrydgard/ppsspp/pull/5668 https://github.com/hrydgard/ppsspp/issues/5686 and suffering several days, audio playing support is finally down! 
The improvements consist of:
1. use ffmpeg to decode audios, more efficient and saint
2. support multiple audios playing simultaneously
3. fully support save/load state without crash and playing audios after loadstate.

Here is a proper commit for you to merge. Thanks a lot for @hrydgard  @unknownbrackets and everyone who have joint the disscusion and give suggestions. I've also learn so much during this project and understand better and deeper the stucture and the functionality of the ppsspp! Thanks again for all your supports, helps and accompanies during these days.