port: revert multithreaded audio experiments

until I can figure out how to fix all the funny concurrency issues that cropped up

port/include/audio.h

@@ -6,6 +6,7 @@
 s32 audioInit(void);
 s32 audioGetBytesBuffered(void);
 s32 audioGetSamplesBuffered(void);
-void audioSubmitBuffer(const s16 *buf, u32 size);
+void audioSetNextBuffer(const s16 *buf, u32 len);
+void audioEndFrame(void);
 
 #endif