Set initial udfps alpha state to 0f

To avoid flicker of icon when it's first attached
in case it shouldn't be immediately shown. The transition
will be the first to update the view's alpha.

Test: manually enable udfps refactor, enroll udfps,
observe transition between home => AOD
Bug: 278719514

Change-Id: I752008928cd619c3b32af8b5b0164292bc23d662