Update tier names in biometric constants documentation

Adds references to the new security tier names (Tier 1/2/3) in the
documentation for the corresponding biometric authenticator constants:
- Strong -> Tier 3
- Weak -> Tier 2
- Convenience -> Tier 1

Test: Builds
Fixes: 157266312
Change-Id: I80965e8e5c53f049d91f18f0e114d89f18593400