Board Thread:Plants vs. Zombies 2: It's About Time/@comment-25369233-20141101122834/@comment-25200219-20141104113619

GMD Auto Hide Soft Keys (Root needed)

It worked perfect for me.

You can try other "hide softkeys" apps which doesn't require root access (for example Softkeys Ninja or GMD Full Screen Immersive Mode ) but I hasn't tried them yet.