Update UnlockMethodCache when screen turns off

Fixes: 65212307

Test: 1) add a temporary log in update()
2) turn off screen, make sure update() is called, and
   canSkipBouncer value is updated and correct

Change-Id: I576d2375d38e83f286ad1fc6aa25944326c3ef8f
(cherry picked from commit 08ae6643)