Always show the DPM locked by admin message

If the DPM locked the device, we always want to show
the "Device locked by admin" message. Previously,
the message would only show if there were trust agents
enabled or a biometric enrolled.

Test: manually lock device with DPM w/o a biometric or trust
agents enabled. See message in bouncer.
Test: atest KeyguardViewMediatorTest
Fixes: 188439183

Change-Id: I0fcee0646da11d4bc63b8224eb4cda2bb6c495c9