Store ambient display suppression state in memory.

We were previously using a secure setting, which means that the
suppression state would be persisted across reboots.

Test: atest SystemUITests, atest FrameworksServicesTests:PowerManagerServiceTest
Change-Id: I3016bdabc67c15b8759a78ce92f4d9262b1380a3
Bug: 147587449
(cherry picked from commit 05f9538c)