Fix 2797185: Show 3D Recents on xlarge device

This fixes a bug where some xlarge devices weren't showing 3D recent apps.
The cause was that the config wasn't guaranteed to be loaded by
the time we reach init() in PhoneWindowManager.

The fix looks at the property on-demand, which can't happen
until after the user sees the home screen, which guarantees the
configuration is loaded.

Change-Id: Ic41196f7a15218033b831e6e9cf9d536e0712844