FRP: Add migration for upgrading from a version without FRP credential

Adds logic to migrate the device owners credential to
the persistent data block if the device has been upgraded
from a version without FRP credential to one with.

Change-Id: I239aaf64506969d60eba8098bfceb24f846ccc94
Fixes: 63039966
Test: Migrate phone from OC-DR1 build. Factory reset. Verify FRP credential works.