examples/mtdpart:Register MTD devices using the mtd_register method

1. Due to the automatic wrapping of MTD devices during the open() process,
   the legacy registration methods ftl_initialize() and bchdev_register()
   are no longer required for MTD device registration. The new method is
   now changed to register_mtddriver

2. Some code for space release and deregistration has been added,
   and certain error handling methods have been updated.

Author: jingfei195887