Update bouncer visibility on altAuthBouncer changes

Previously when the UDFPS bouncer disappeared,
the UdfpsKeyguardViewController wouldn't appropriately
update its state, so it wouldn't reappear. This fixes
that issue.

Test: atest SystemUITests
Test: manual
Fixes: 223693990
Change-Id: I303328cd82677cf964d143b447676dba9a255dc4