HID: hid-appletb-kbd: add support for automatic brightness control while using the touchbar

On Windows, if there is no input by the user for 60 sec, the Touch Bar dims
automatically, and after further 15 sec, it turns off. On receiving input,
the Touch Bar resets the timer and goes back to full brightness. This patch
implements the same functionality.

Signed-off-by: Aditya Garg <gargaditya08@live.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>