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>

drivers/platform/x86/thinkpad_acpi.c

@@ -3171,8 +3171,10 @@ static int __init hotkey_init(struct ibm_init_struct *iibm)
 		KEY_MICMUTE,	/* 0x1a: Mic mute (since ?400 or so) */
 
 		/* (assignments unknown, please report if found) */
-		KEY_UNKNOWN, KEY_UNKNOWN, KEY_UNKNOWN, KEY_UNKNOWN,
 		KEY_UNKNOWN,
+
+		/* Extra keys in use since the X240 / T440 / T540 */
+		KEY_CONFIG, KEY_SEARCH, KEY_SCALE, KEY_COMPUTER,
 		},
 	};