HID: asus: Add support for 2021 ASUS N-Key keyboard

Some new 2021 version of ASUS gamer laptops are using an updated
N-Key keyboard with the PID of 0x19b6. This version is using the
same init sequence and brightness control as the 0x1866 keyboard.

Signed-off-by: Luke D Jones <luke@ljones.dev>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>