Does new drywall need 2 coats of primer
It really depends on the results you get after the first coat.  The purpose of primer is to lay down a surface that is uniform and consistent in


color, within reason
smoothness 
texture
absorption
absence of surface contamination


Because if those things are not uniform, the irregularities will print through when you topcoat.  

You can get it to stop printing through if you spam enough coats of topcoat... But since that's primer's job, it's better to resolve it at the primer stage, where you are sure to get it in 1 or 2.