Ability to disable hardware keys via nav bar settings (2/2)

Change-Id: Ib52a7db62b8d7d66ba4476873e37752f79a19813
Add android:key in hardware keys enable/disable option to forward ena…
…ble this option in devices with hardware keys and not in devices
without.

- Check devices related core/res/res/values/cr_config.xml to enable or
disable
Change-Id: I3f44cb8626c058d968c479921374baf9cc796c82