Audio emulation out of sync

[clbr]

1. App submits a large audio buffer, several seconds+
2. cen64 plays it realtime, and immediately requests more, even though emulation is otherwise at 26fps

This leads to the app getting the audio interrupt way early, affecting its behavior.

Two solutions:

1. Slow down the playback to match emulation speed
2. Play at realtime, but wait with silence, and only request more when it's time to do so

I do realize the current behavior may make commercial games sound better, if they manage to play skipless music despite being 20fps otherwise, but it's an inaccurate hack. If someone cares, it could be kept under some -gamehacks option.