Don't draw behind the display cutout in keyguard

Add layout mode to KeyguardStatusBarView so that it can behave exactly
as it used to when there is no cutout, but have reasonable behavior when
there is.

Test: visual with/without cutout and with/without multi-user switch
Fixes: 72683977
Fixes: 72388285

Change-Id: I72ae5a581dd9d1884ffaf5332f7490d806d319b5