audio: Add overlay to fix analog docks.

Of particular interest to devices using libhardware_legacy and
affected by commit 5a484b753cc72d6a50c1dd3bbf68b3403c741a3a: http://goo.gl/rVR1Z
which restricted the routing of AUDIO_DEVICE_OUT_ANLG_DOCK_HEADSET
to docks using FORCE_ANALOG_DOCK cases. The EXTRA_DOCK_STATE_CAR case is
returning FORCE_BT_CAR_DOCK, preventing the dock audio from routing properly.

Add an overlay option for overriding to FORCE_ANALOG_DOCK.

Change-Id: Ib7d70c242aa6f537ea5d65098ceb2c591662d8bb