Restore AOD after SysUI Restart.

If the device was sleeping when SystemUI restarts, it would lose its
connection to loze its connection to the DreamService.

With this cl, we store when the device was dreaming and attempt to
reconnect when sysui restarts. This happens particularly when Flags
change.

Fixes: 268060399
Test: manual
Change-Id: Ie8583a6bbf9522d3a0fe2e5d3cfd94c43cc48f8d