x86-geode does not include the common x86 target-settings. Thus we need
to specify the device class in order to build images with all necessary
packages included.

The old bash-based parsing code was way too complex. Replace it with Lua.

This allows for smaller firmware images and makes it possible to reset a
device via firstboot command.

Signed-off-by: Matthias Fritzsche <matthias@chemnitz.freifunk.net>