Move more code out of main-nrf52 into variant.cpp (#9450)

variants/nrf52840/diy/nrf52_promicro_diy_tcxo/variant.cpp

@@ -36,3 +36,10 @@ void initVariant()
     pinMode(PIN_3V3_EN, OUTPUT);
     digitalWrite(PIN_3V3_EN, HIGH);
 }
+
+void variant_shutdown()
+{
+    nrf_gpio_cfg_input(BUTTON_PIN, NRF_GPIO_PIN_PULLUP); // Enable internal pull-up on the button pin
+    nrf_gpio_pin_sense_t sense = NRF_GPIO_PIN_SENSE_LOW; // Configure SENSE signal on low edge
+    nrf_gpio_cfg_sense_set(BUTTON_PIN, sense);           // Apply SENSE to wake up the device from the deep sleep
+}