The magic system will do. People are taking the system's name too literally, perhaps I should change it. :P I define it as any supernatural force, personally, be it divine or arcane in origin.
So yes, you would use the magic system to define your paladin's boundaries in terms of preps and the power of his divine skills. You could have something like 10 max preps and 5 in holy power.
oli kaiken nähny, kaiken kuullu, kaiken tiänny