fix(el18): Audio output should be OFF if no audio playing (#3670)

* Added audio on/off depends whether audio content is present.

* Aligned the mute control with the implementation in the DAC driver.

* Mute Pin should be inverted.

* Removed PCB specific dependencies.

* chore: Formatting and cleanup

radio/src/audio.cpp

@@ -525,8 +525,6 @@ void audioTask(void * pdata)
 #if defined(PCBX12S) || defined(RADIO_TX16S)
   // The audio amp needs ~2s to start
   RTOS_WAIT_MS(1000); // 1s
-#elif defined(PCBNV14)
-  audioOn();
 #endif
 
   while (true) {