asus-grouper: update to use devicepkg-dev

Updated the device-asus-grouper package to use devicepkg-dev (#8 (closed))

I've tested the resulting image and it builds, boots and has a working touchscreen (in Weston)

I've also noticed that the device reboots itself at times, both in the USB ssh console and in Weston. This seems to be a known issue but I don't know how prevalent it was before.

It would be great if someone else could test this to confirm that it works.