add board_test example for testing new board

hw/bsp/feather_nrf52840_express/feather_nrf52840_express.c

@@ -67,10 +67,12 @@ void board_init(void)
   SysTick_Config(SystemCoreClock/1000);
 #endif
 
+#if TUSB_OPT_DEVICE_ENABLED
   // Priorities 0, 1, 4 (nRF52) are reserved for SoftDevice
   // 2 is highest for application
   NVIC_SetPriority(USBD_IRQn, 2);
 
+
   // USB power may already be ready at this time -> no event generated
   // We need to invoke the handler based on the status initially
   uint32_t usb_reg;
@@ -103,6 +105,7 @@ void board_init(void)
 
   if ( usb_reg & POWER_USBREGSTATUS_VBUSDETECT_Msk ) tusb_hal_nrf_power_event(NRFX_POWER_USB_EVT_DETECTED);
   if ( usb_reg & POWER_USBREGSTATUS_OUTPUTRDY_Msk  ) tusb_hal_nrf_power_event(NRFX_POWER_USB_EVT_READY);
+#endif
 }
 
 //--------------------------------------------------------------------+