I think you can take these two multiple times.
Just not for the same school.
Or every enchanter ever would only take Spell Focus(Enchantment). +whatever to EVERY enchantment DC? Yes, thank you!
I'd say that every Spell Focus or Varisian Tattoo is a sub-feat based on which school you choose, so each can be taken once. Of course, what Torbyne said is probably more to RAW.