HID: apple: Report Magic Keyboard battery over USB

When connected over USB, the Apple Magic Keyboard 2015 registers 3
different interfaces. One of them is used to report the battery level.

However, unlike when connected over Bluetooth, the battery level is not
reported automatically and it is required to fetch it manually.

Add a new quirk to fix the battery report descriptor and a timer to
fetch the battery level.

Signed-off-by: José Expósito <jose.exposito89@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>