nrf: microcontroller: use port reset path

For `microcontroller.reset()`, don't manually call NVIC_SystemReset().
Instead, call the `port_reset()` in case the port wants to do any
cleanup.

Signed-off-by: Sean Cross <sean@xobs.io>

ports/nrf/common-hal/microcontroller/__init__.c

@@ -94,7 +94,7 @@ void common_hal_mcu_on_next_reset(mcu_runmode_t runmode) {
 
 void common_hal_mcu_reset(void) {
     filesystem_flush();
-    NVIC_SystemReset();
+    reset_cpu();
 }
 
 // The singleton microcontroller.Processor object, bound to microcontroller.cpu