Merge pull request #532 from KurtE/mtp_event_usb_desc_only

T3/T4.x MTP device descriptor - update endpoint and size

teensy3/usb_desc.h

   #define MTP_RX_ENDPOINT	3
   #define MTP_RX_SIZE		64
   #define MTP_EVENT_ENDPOINT	4
-  #define MTP_EVENT_SIZE	16
+  #define MTP_EVENT_SIZE	32
   #define MTP_EVENT_INTERVAL	10
   #define SEREMU_INTERFACE      1	// Serial emulation
   #define SEREMU_TX_ENDPOINT    1
   #define ENDPOINT1_CONFIG	ENDPOINT_TRANSMIT_ONLY
   #define ENDPOINT2_CONFIG	ENDPOINT_RECEIVE_ONLY
   #define ENDPOINT3_CONFIG	ENDPOINT_TRANSMIT_AND_RECEIVE
-  // TODO: Should ENDPOINT4_CONFIG be ENDPOINT_TRANSMIT_ONLY ???
-  #define ENDPOINT4_CONFIG	ENDPOINT_RECEIVE_ONLY
+  #define ENDPOINT4_CONFIG	ENDPOINT_TRANSMIT_ONLY
 
 #elif defined(USB_AUDIO)
   #define VENDOR_ID		0x16C0

teensy4/usb_desc.h

   #define MTP_RX_SIZE_12	64
   #define MTP_RX_SIZE_480	512
   #define MTP_EVENT_ENDPOINT	4
-  #define MTP_EVENT_SIZE	16
+  #define MTP_EVENT_SIZE	32
   #define MTP_EVENT_INTERVAL_12	10	// 10 = 10 ms
   #define MTP_EVENT_INTERVAL_480 7	// 7 = 8 ms
   #define SEREMU_INTERFACE      1	// Serial emulation
   #define SEREMU_RX_INTERVAL    2
   #define ENDPOINT2_CONFIG	ENDPOINT_RECEIVE_INTERRUPT + ENDPOINT_TRANSMIT_INTERRUPT
   #define ENDPOINT3_CONFIG	ENDPOINT_RECEIVE_BULK + ENDPOINT_TRANSMIT_BULK
-  // TODO: Should ENDPOINT4_CONFIG be ENDPOINT_RECEIVE_UNUSED + ENDPOINT_TRANSMIT_INTERRUPT ???
-  #define ENDPOINT4_CONFIG	ENDPOINT_RECEIVE_INTERRUPT + ENDPOINT_TRANSMIT_UNUSED
+  #define ENDPOINT4_CONFIG  ENDPOINT_RECEIVE_UNUSED + ENDPOINT_TRANSMIT_INTERRUPT
 
 #elif defined(USB_AUDIO)
   #define VENDOR_ID		0x16C0