This photo from AllAroundOrlando caught what appears to be a single doorway on the otherwise blank wall in the recess to the right of King's Cross (far right bottom). I'm guessing it will look like the picture Felipe just posted^ and be access to the Leaky Cauldron. Not a main entrance,or even a marked entrance apart from the small hanging sign, but there for authenticity's sake and as a hidden bonus for knowledgeable fans.
And the plans do show a doorway there, opening into the area that is the Leaky Cauldron.