Reorganized the biometric weak check functions

Moved isBiometricSensorAvailable functionality into
isBiometricWeakInstalled (formerly called isBiometricEnabled).  Settings
now only shows biometric weak if it's installed, if it's not installed
and the lock type is currently set to biometric weak, the backup lock
is shown as being set instead.

Change-Id: Icfe326a6598df33ee60d5fdc024273d94f115983