Revert "remove disable navkeys option"

Disabling hardware buttons with a single checkbox at a kernel level >>> setting them all to "do nothing" actions. Neither is reversible with a toggle.

This reverts commit c16d17dde97fc112e3a5085be0a6d7f1fa10d69e.

Change-Id: I8c9fd77cd67628cf5f76e69bbabf7cbde6069f97