lazy load enrollment application UID in VIMS

Enrollment application services are only avaiable for package manager
to query after the system on-boot-completed status. Lazy loading the
KeyphraseEnrollmentInfo class until first client access ensures all
packages are loaded prior to query.

Bug: 151095585
Test: erase userdata and boot device; ensure no enrollment application
crashes when boot device for first time; dump enrollment database with
`dumpsys voiceinteraction` and confirm model is present in database.

Change-Id: I6009d5834fff8848a17e5edef9d39395b1586318