support Thinkpad X1 Carbon 2nd generation's adaptive keyboard

Submit patch V4 to support Adaptive Keyboard on Thinkpad X1 Carbon 2nd
generation according to Tobias's comments.

Thanks,
Shuduo

>From b153a7b14791c6e01892c0e274e23eefd625fb8d Mon Sep 17 00:00:00 2001
From: Shuduo Sang <shuduo.sang@canonical.com>
Date: Mon, 3 Mar 2014 14:29:32 +0800
Subject: [PATCH] support thinkpad X1 Carbon's adaptive keyboard

Thinkpad X1 Carbon's adaptive keyboard has five modes including Home
mode, Web browser mode, Web conference mode, Function mode and Lay-flat
mode. We support Home mode and Function mode currently.

Signed-off-by: Bruce Ma <bruce.ma@canonical.com>
Signed-off-by: Shuduo Sang <shuduo.sang@canonical.com>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>