thinkpad_acpi: Update mapping for F12 hotkey on *40 models to KEY_FILE

The new keyboard found on the *40 models is also being sold as a standalone
keyboard (with trackpoint):
http://shop.lenovo.com/us/en/itemdetails/0B47189/460/60AC6A0372B14F5BA7B12F1FF88E33C7



This uses a standard HUT code for the F12 key with the 6 square boxes on it,
which gets mapped to KEY_FILE by the kernel. Change the mapping done of
identical laptop key done by thinkpad_acpi to also send KEY_FILE for
consistency.

Cc: Jamie Lentin <jm@lentin.co.uk>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>