Use allowPrivateProfile to guard BiometricFragment changes

The BiometricPrompt API setAllowBackgroundAuthentication is
now guarded by allowPrivateProfile flag. This change ensures the
references to this API are flagged by the same flag, and the uber
private space implementation flag - enablePrivateSpaceFeatures, as
well.

Bug: 312184187
Test: Tested by flashing changes on a test device
Flag: Flags.ALLOW_PRIVATE_PROFILE
Change-Id: Icfdc5a2c2f07177c25fa3d545837052209b76551