HID: lg-g15: Add support for the Logitech Z-10 speakers

Add support to hid-lg-g15 for the Logitech Z-10 speakers. This adds
support for the LCD menu keys found on these speakers, as well as
support for controlling the LCD's brightness through a LED classdev.

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