Add config option for permanent dpad presence.

Since all TV devices are required to have a DPad as a form of
navigation we should suppress any configuration instances where it
claims one doesn't exist just because it isn't currently connected.

This prevents applications from going through a configuration change
and potentially an app restart when a remote disconnects to save
battery.

Bug: 17493314
Change-Id: Ice87b7056984afe02917ccba9196fdbcac9985fc