From enlarge person,
Multiple magical effects that increase size do not stack.
But the evolution Large is listed as (Ex), making it non-magical. And greater evolution surge isn’t increasing the eidolon’s size, the non-magical Large evolution is doing that.
So, rules as written, I agree that enlarge person, when applied to an eidolon who already has the Large evolution, should make that eidolon Huge. Whether or not the Large evolution came from greater evolution surge is, as far as I can tell, completely irrelevant.
Whether or not I would actually allow that, or any other GM would, I’m less sure. Enlarge person has a lot of problems (most importantly that casting time), so I’m not convinced that this is a problem, but eidolons are pretty powerful as it is.