Align NSSL bottom to barrier

This will allow for proper notification sizing when the lock icon
and/or the ambient indication area are present.

Fixes: 308772985
Manual: Observe layouts in both default and splitshade blueprints, in
both orientations
Flag: ACONFIG com.android.systemui.keyguard_shade_migration_nssl
DEVELOPMENT

Change-Id: I9c9bd894933a2f0157f5a4eeae19ec596ecf307d