limit voices by default, add some drums

quantum/audio/voices.h

@@ -11,6 +11,7 @@ float voice_envelope(float frequency);
 
 typedef enum {
     default_voice,
+    #ifdef AUDIO_VOICES
     something,
     drums,
     butts_fader,
@@ -23,6 +24,7 @@ typedef enum {
     // duty_fourth_down,
     // duty_third_down,
     // duty_fifth_third_down,
+    #endif
     number_of_voices // important that this is last
 } voice_type;