AP_Notify: define external led pins for non APM boards

resolves compiler errors

libraries/AP_Notify/ExternalLED.h

@@ -32,6 +32,11 @@
  #define EXTERNAL_LED_ARMED   65    // Armed LED - AN11
  #define EXTERNAL_LED_MOTOR1  62    // Motor1 LED - AN8
  #define EXTERNAL_LED_MOTOR2  66    // Motor2 LED - AN12
+#else
+ #define EXTERNAL_LED_GPS     0     // pin definitions to allow this lib to build for
+ #define EXTERNAL_LED_ARMED   0     // for other boards besides APM1, APM2 even though
+ #define EXTERNAL_LED_MOTOR1  0     // they will never be used
+ #define EXTERNAL_LED_MOTOR2  0
 #endif
 
 class ExternalLED