As a follow-up to Christian’s post, it is possible to hide the entire chrome within an Android app, e.g. for a video viewer app. Android however automatically fades in the navigation buttons as soon as the user touches the screen, so this is not really an option for a game.
If you still want to implement that behavior you have to implement your own Activity and set the base class to QtActivity (or VPlayActivity if you use any of our plugins). Please see this post from Sony as a reference: http://developer.sonymobile.com/knowledge-base/tutorials/android_tutorial/how-to-provide-your-app-users-with-maximum-screen-estate-tutorial/