Refine checkMaxEnrolled() for fingerprint

FingerprintEnrollIntroduction shall allow setting 2nd fingerprint if
this intent is coming from "Anything else" page in SUW.

Bug: 228418807
Test: Manually test fingerprint in SUW
Test: ROBOTEST FingerprintEnrollIntroduction and
      SetupFingerprintEnrollIntroduction
Change-Id: I62edeb91f90b32f62b3ca2b2ea04ec427b31d483