Fixes 'no ripple effect' issue for screen attention setting

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