adding msc Start Stop to buitin command, but not complate yet

add tud_msc_start_stop_cb() as optional callback

examples/device/cdc_msc_hid_freertos/src/msc_disk.c

@@ -152,6 +152,26 @@ void tud_msc_capacity_cb(uint8_t lun, uint32_t* block_count, uint16_t* block_siz
   *block_size  = DISK_BLOCK_SIZE;
 }
 
+// Invoked when received Start Stop Unit command
+// - Start = 0 : stopped power mode, if load_eject = 1 : unload disk storage
+// - Start = 1 : active mode, if load_eject = 1 : load disk storage
+void tud_msc_start_stop_cb(uint8_t lun, uint8_t power_condition, bool start, bool load_eject)
+{
+  (void) lun;
+  (void) power_condition;
+
+  if ( load_eject )
+  {
+    if (start)
+    {
+      // load disk storage
+    }else
+    {
+      // unload disk storage
+    }
+  }
+}
+
 // Callback invoked when received READ10 command.
 // Copy disk's data to buffer (up to bufsize) and return number of copied bytes.
 int32_t tud_msc_read10_cb(uint8_t lun, uint32_t lba, uint32_t offset, void* buffer, uint32_t bufsize)