HID: asus: Add support for Zen AiO MD-5110 keyboard

Add support for media keys on the MD-5110 wireless keyboard that comes
with the Asus V221ID and ZN241IC All In One computers.

The keys to support here are WLAN, BRIGHTNESSDOWN and BRIGHTNESSUP.

The USB Vendor ID suggests that it is a TURBOX device, but
the physical branding only mentions ASUS MD-5110.

Signed-off-by: Daniel Drake <drake@endlessm.com>
Acked-by: Benjamin Tissoires <benajmin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>