Plane: move relay init earlier

allows relay pins to be used as pullups for other sensors (such as
LidarLiteV3)

ArduPlane/system.cpp

@@ -139,6 +139,8 @@ void Plane::init_ardupilot()
     // setup any board specific drivers
     BoardConfig.init();
 
+    relay.init();
+
     // initialise notify system
     notify.init(false);
     notify_flight_mode(control_mode);
@@ -216,8 +218,6 @@ void Plane::init_ardupilot()
 
     init_rc_in();               // sets up rc channels from radio
 
-    relay.init();
-
 #if MOUNT == ENABLED
     // initialise camera mount
     camera_mount.init(&DataFlash, serial_manager);