variants: XIAO NRF52: Enable user button

The Xiao nRF52840 combined with the Wio-SX1262 is often used for
cheap and compact DIY companion nodes. The Wio actually has an onboard
pushbutton that can be used as user button. Enable support for the
button.

Signed-off-by: Frieder Schrempf <frieder@fris.de>

variants/xiao_nrf52/target.cpp

@@ -2,6 +2,10 @@
 #include "target.h"
 #include <helpers/ArduinoHelpers.h>
 
+#ifdef DISPLAY_CLASS
+  DISPLAY_CLASS display;
+#endif
+
 XiaoNrf52Board board;
 
 RADIO_CLASS radio = new Module(P_LORA_NSS, P_LORA_DIO_1, P_LORA_RESET, P_LORA_BUSY, SPI);