This patch migrates the USB LED driver to the HID subsystem.
Supported are Dream Cheeky Webmail Notifier / Friends Alert
and Riso Kagaku Webmail Notifier.

Benefits:
- Avoid using USB low-level calls and use the HID subsystem instead
  (as this device provides a USB HID interface)
- Use standard LED subsystem instead of proprietary sysfs entries,
  this allows e.g. to use the device with features like triggers

Successfully tested with a Dream Cheeky Webmail Notifier and a
Riso Kagaku Webmail Notifier compatible device.
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>