add optional event hook callback tud_event_hook_cb() and tuh_event_hook_cb()

src/device/usbd.h

@@ -146,6 +146,9 @@ TU_ATTR_WEAK void tud_suspend_cb(bool remote_wakeup_en);
 // Invoked when usb bus is resumed
 TU_ATTR_WEAK void tud_resume_cb(void);
 
+// Invoked when there is a new usb event, which need to be processed by tud_task()/tud_task_ext()
+TU_ATTR_WEAK void tud_event_hook_cb(uint8_t rhport, uint32_t eventid, bool in_isr);
+
 // Invoked when received control request with VENDOR TYPE
 TU_ATTR_WEAK bool tud_vendor_control_xfer_cb(uint8_t rhport, uint8_t stage, tusb_control_request_t const * request);