Preferences shouldn't be initialized at onAttach() because the settings
style hasn't been loaded yet. This change defers the preferences
initialization so that they comply with the settings style.
Test: manually
Test: make RunSettingsRoboTests ROBOTEST_FILTER=com.android.settings.display
Bug: 183909540
Change-Id: I4dc4503924a1dcd5b8d41f7d27e576befb11f976