HID: lenovo: Factor out generic parts of the LED code

Factor out the generic parts of the tpkbd LED code, so that they can be
re-used for supporting the LEDs on the Thinkpad 10 ultrabook kbd.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>