Allow trust agents to actively unlock for automotive.

This CL creates an exception for the default behavior of trust agents.

After b/120871688, trust agents can only extend unlock. However,
automotive still requires active unlock for its feature set.

Fixes: 135931998
Test: Verify that an enrolled trust agent can dismiss the lock screen
on automotive.

Change-Id: Ie7c411ac2bfac9ba00c095532d6788d9e2e7af2f