lge_touch_core: Allow disabling the nav keys

picked from https://github.com/CyanogenMod/lge-kernel-gproj/commit/cd7ad350d6c37d7d12b32bf08cc527ee8dd6e355

Change-Id: Ibd640bfff4862b1c35120419b672a51623181d0f
Merge pull request #2 from xxxifan/kitkat

lge_touch_core: Allow disabling the nav keys