Migrate DisplayFoldController fold state to be based on device state.

This modifies DisplayFoldController to base it's internal 'fold' state
from being configured directly based on the lid switch (or the proximity
sensor) to be based on the device state.

Bug: 159401801
Test: Manual - fold/unfold and validate fold state

Change-Id: Ib3ecc6326b1d73720d31fa94f33160cfaf1109cd