Persistent audio mute support (#1161)

* Persistent speaker mute support #1100
* Moving persistent mute support from WM8731/AK4951 codec files to audio.cpp module for simplification

firmware/application/audio.hpp

@@ -65,6 +65,8 @@ void stop();
 void mute();
 void unmute();
 
+void speaker_disable();
+void speaker_enable();
 void speaker_mute();
 void speaker_unmute();