Only enforce secure FRP mode when in setup wizard

SUW can be skipped on debug builds and that will leave
secure_frp_mode uncleared, causing credential change
to fail under the current enforcement. Fix it such that
the enforcement only applies before SUW completes.

Bug: 152587445
Test: manual
Change-Id: Ic79a9412a2a11f5a2fcca2b8ea76fdab78496d06