su: Add Root access app-ops control

Adds an app-ops option for root access.

Platform-signed apps weren't previously being listed but there are some
that use root access (FileManager comes to mind).

So we list all of them, but for platform-signed apps we only show the
root toggle and none of the permission-based ones.

Change-Id: Ie716974156d55eb66061e78dc39505569e5bdc2a