cardem: reset the uC in case of USB disconnect

This fixes the firmware USB interface somehow getting stuck
after a USB disconnect/reconnect without power cycle.

Right now there are a number of things we only execute the first time we
reach USBD_STATE_CONFIGURED, but not at any subsequent such event.

It's also rather clear that this doesn't really show in simtrace2 as it
is bus-powered. And it doesn't show on OWHW as we don't have any USB
unplug situations of the USB between the on-board traces of USB host and
SAM3S.  So this really only is relevant to QMOD.

A cheap and dirty work-around is to simply reset the entire uC every
time a USB unplug happens.

Change-Id: I6678bb2192c1419ed388b46c4ae7aa1ce18dc7ee
Related: OS#5578

firmware/apps/cardem/main.c

@@ -206,6 +206,10 @@ extern int main(void)
  if (isUsbConnected) {
  isUsbConnected = 0;
  }
+ /* HACK: we don't really deal with USB disconnect yet,
+ * so let's just reset the entire uC if this happens */
+ TRACE_INFO("Resetting uC on USB disconnect\n\r");
+ NVIC_SystemReset();
  } else if (isUsbConnected == 0) {
  TRACE_INFO("USB is now configured\n\r");