Even though rumors last week suggested that DC and Warner Bros.'s epic next film might in fact be split into two films, Henry Cavill has put that rumor to bed. So, no, Superman v. Batman: Dawn of Justice, while having enough title for two films, will only be one.
Even at the time, it seemed supremely unlikely that Warner Bros. would have spent all this time and money marketing Dawn of Justice if that was the name of the second film and not the one we would see first. The rumor also put the first of the two films as coming out this October, which is a very tight production time.
So now we know that, as far as the film's star knows, it's still just one film.