nrf/drivers/usb: Add USBD_IRQHandler which calls tud_int_handler.

This is needed for TinyUSB to process USB device IRQs.

Related to #6325.
Signed-off-by: Damien George <damien@micropython.org>

ports/nrf/drivers/usb/usb_cdc.c

@@ -223,4 +223,8 @@ void mp_hal_stdout_tx_strn_cooked(const char *str, mp_uint_t len) {
     }
 }
 
+void USBD_IRQHandler(void) {
+    tud_int_handler(0);
+}
+
 #endif // MICROPY_HW_USB_CDC