Enable touch feedback vibrations on silent mode.

Keep behavior from Android S to allow touch vibrations while phone is on
silent or DnD modes. Users will now be able to toggle this user settings
if they want to disable them, which was not available in S.

Fix: 165478128
Test: VibrationSettingsTest
Change-Id: I48c24493b1db53c9b7a99d7b8a916bbbc8ad2d88