SystemUI: improve lockscreen tile behavior with profiles

Disable (grey out) the lock screen tile when a profile is already
disabling it. Profiles takes precedence over the internal setting.

Also simplify lockscreen disable logic - using a null'd Boolean without
synchonization will lead to things falling out of place.

Ref: CYNGNOS-1930

Change-Id: Ia4cb7926e418a4d72426be65e5bfb11dc44bee5e
Signed-off-by: Roman Birg <roman@cyngn.com>