Initial support for the ICPad

- Basic support for up to 4 ISSI chips (and partial support for 16 chip configurations)
- Initial USB mux support
  * Required USB re-init procedure
- Initial interconnect mux support
  * Required some state reset commands

Output/pjrcUSB/arm/usb_dev.c

@@ -1176,6 +1176,9 @@ uint8_t usb_init()
 	print("USB INIT"NL);
 	#endif
 
+	// Unset usb configuration
+	usb_configuration = 0;
+
 	// Clear out endpoints table
 	for ( int i = 0; i <= NUM_ENDPOINTS * 4; i++ )
 	{