Allow an app to drive permission backup+restore

In AOSP the permission backup+restore is driven by the system server,
but some OEMs might drive it from an app. Hence allow a privilidged app
to backup + restore permission backups.

Test: atest CtsBackupTestCases
Fixes: 141007569
Change-Id: Ic89b476948872c491de8ea54b83667afc0183bb4
7 files changed