I noticed a weird thing about that, in Intel XDK Preview, tapping on a textbox does let the layer scroll up to see the textbox.
But after exporting it with Crosswalk and installing the app on your device, it no longer scrolls the layer up when the textbox is focused.
This seems to be an issue with Crosswalk export.
-EDIT-
You can try to scroll the layer by event to show the textbox, but I'm not sure if it conflicts with any sceensize support options.