New unplugged callback & event filtering

- A USB event is only added when it's new and different from the last unhandled one
- New event to inform when the device is unplugged on USB (like when the PHY is reset)

src/device/usbd.c

@@ -531,6 +531,11 @@ void tud_task_ext(uint32_t timeout_ms, bool in_isr)
         else if (DCD_EVENT_UNPLUGGED == event.event_id)
         {
           _usbd_dev.speed = DCD_EVENT_INVALID;
+
+          if (tud_unplugged_cb)
+          {
+            tud_unplugged_cb();
+          }
         }
       break;
 

src/device/usbd.h

@@ -142,6 +142,9 @@ TU_ATTR_WEAK void tud_mount_cb(void);
 // Invoked when device is unmounted
 TU_ATTR_WEAK void tud_umount_cb(void);
 
+// Invoked when device is unplugged
+TU_ATTR_WEAK void tud_unplugged_cb(void);
+
 // Invoked when usb bus is suspended
 // Within 7ms, device must draw an average of current less than 2.5 mA from bus
 TU_ATTR_WEAK void tud_suspend_cb(bool remote_wakeup_en);