Check portal on fingerprint intro page

Check SUW portal flag on Fingerprint introduction page. Do not use
suw_max_fingerprints_enrollable as fingerprint count if portal flag is
enable.

Bug: 235655422
Test: m RunSettingsRoboTests \
      ROBOTEST_FILTER=FingerprintEnrollIntroductionTest
Test: Manually test "Add another finger" on Deferred and Portal
      suggested actions page
Change-Id: I2789d95fb214b5da6d8d03ef77583d064652e69e