system_server: allow restorecon /data/system/users/0/fpdata

Addresses the following denial:

  avc: denied { relabelfrom } for pid=9971 comm="system_server" name="fpdata" dev="dm-0" ino=678683 scontext=u:r:system_server:s0 tcontext=u:object_r:system_data_file:s0 tclass=dir permissive=0

Bug: 25801240
Change-Id: I043f48f410505acaee4bb97446945316f656a210