- Add a special list to the MSD state and add pointers to the runtime-only
options for the cdrom. The restore handler of this list calls runtime_config()
to make sure the media path and status are correctly updated.
- Registering a runtime config handler for the USB cdrom is not necessary since
runtime_config() is always called from the hub it is connected to.
- Restore a string parameter value only if it's different from the initial one.