Allow keyguard to be locked while dreaming

Currently when a device is folded in the unlocked state, keyguard is
forced to be in the unlocked state. This change resets this state when
dream starts to keep the device secure.

Test: atest KeyguardUpdateMonitorTest
Test: verified after dream starts in the folded, unlocked state, the
      device gets locked 5 seconds after dream starts, based on the
      default lock after screen timeout setting
Fix: 415210679
Flag: EXEMPT bug fix
Change-Id: I5f6eacee32b8c245e91583d9edcf1a2ba1332ae1