Update usb.c

configure usb_mtp also from usb.c

teensy4/usb.c

 #include "usb_touch.h"
 #include "usb_midi.h"
 #include "usb_audio.h"
+#include "usb_mtp.h"
 #include "core_pins.h" // for delay()
 #include "avr/pgmspace.h"
 #include <string.h>
 		#if defined(AUDIO_INTERFACE)
 		usb_audio_configure();
 		#endif
+		#if defined(MTP_INTERFACE)
+		usb_mtp_configure();
+		#endif
 		#if defined(EXPERIMENTAL_INTERFACE)
 		endpoint_queue_head[2].unused1 = (uint32_t)experimental_buffer;
 		#endif