SystemUI: visually disable EditTile in lock screen

It's unclear that the edit tile toggle will not be functional in the
lock screen - reflect this by disabling the tile when on the keyguard.

Ref: OPO-426

Change-Id: I9ec46402b8d63e012ca806bafa4c050fc0729ab8
Signed-off-by: Roman Birg <roman@cyngn.com>
(cherry picked from commit 0358395c)