Tweak paramters of mp3_play_data and callback.

Use generic void * and size_t and make mp3_play_data and its callback
agree on types. Use mp3_play_callback_t instead of prototyping
right in the function call (so it's not so messy to look at). Change
doesn't appear to require plugin API version increment.

Change-Id: Idcab2740ee316a2beb6e0a87b8f4934d9d6b3dd8
13 files changed