thinkpad_acpi: Add mappings for F9 - F12 hotkeys on X240 / T440 / T540

The T440s user guide says that when Fn-lock is not active, the *40s' F9 - F12
keys should be mapped to: control-panel, search, show-all-windows and Computer.

These keys generate the sofar unused 28 - 31 hotkey scancodes.

For the first 2 this nicely matches the icons on the keys, for the latter 2
the icons are somewhat creative, which is why I ended up looking them up in
the user manual.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>