imx233: stop watchdog on exception

Change-Id: If11d90343d32d5889857e7ba30a99f60a87639f1

firmware/target/arm/imx233/system-imx233.c

@@ -115,6 +115,8 @@ void system_reboot(void)
 
 void system_exception_wait(void)
 {
+    /* stop hadrware watchdog, IRQs are stopped */
+    imx233_rtc_enable_watchdog(false);
     /* make sure lcd and backlight are on */
     lcd_update();
     _backlight_on();