Implemented beeps on MD-UV3x0 platform driver.

openrtx/src/core/voicePrompts.c

@@ -545,6 +545,7 @@ void vp_beep(uint16_t freq, uint16_t duration)
         duration=2000; 
     
     currentBeepDuration=duration;
+    audio_enableAmp();
     
     platform_beepStart(freq);
     // See BeepTick for termination.

platform/targets/MD-UV3x0/platform.c

@@ -184,13 +184,12 @@ void platform_ledOff(led_t led)
 
 void platform_beepStart(uint16_t freq)
 {
-    /* TODO */
-    (void) freq;
+    toneGen_beepOn((float)freq, 255, 0);
 }
 
 void platform_beepStop()
 {
-    /* TODO */
+    toneGen_beepOff();
 }
 
 const void *platform_getCalibrationData()