Notify AuthController when fingerprint providers are ready

This change introduces a callback that AuthController can provide to
FingerprintService to get notified when all of the fingerprint providers
are available.

This fixes the bug where UDFPS overlay is not available if SystemUI
starts before the fingerprint HAL, because SystemUI would query the
fingerprint providers on startup.

Bug: 184677066
Test: atest AuthControllerTest
Test: on device

Change-Id: I165d67bdda09ea10dd5aac539c4155e6b158227d