[APU] Refactor audio system to work with different frequencies/channel layouts

src/xenia/apu/audio_system.h

@@ -42,7 +42,12 @@ class AudioSystem {
   X_STATUS RegisterClient(uint32_t callback, uint32_t callback_arg,
                           size_t* out_index);
   void UnregisterClient(size_t index);
-  void SubmitFrame(size_t index, uint32_t samples_ptr);
+  void SubmitFrame(size_t index, float* samples);
+
+  // Creates an independent, non-registered driver instance.
+  virtual AudioDriver* CreateDriver(xe::threading::Semaphore* semaphore,
+                                    uint32_t frequency, uint32_t channels,
+                                    bool need_format_conversion) = 0;
 
   bool Save(ByteStream* stream);
   bool Restore(ByteStream* stream);