Eating healthy food in general, plenty of protein and good carbs, good fats and very low on bad fats, etc. (just keeping a healthy diet) will encourage growth (of your whole body) in general.
However, you can't target your diet to specifically grow any one part of your body, including your penis. There are not any foods or herbs that will specifically target penis growth.
And where did you hear soy will stunt penis growth? That's completely untrue. Soy might not be the best to have tons of for other reasons, but it has nothing to do with penis growth.