Enable CM10.1 dock functionality, as defined in framework base

https://github.com/cyanogenmod/android_frameworks_base/commit/4bfdaf9e1436dd6a5c5bbb102fec633d66c2617d
Merge branch 'jellybean_4.2' of github.com:josteink/device_asus_tf101 into jellybean_4.2