Add rfkill package to baseline armv7 minfs tarballs

[sarnold]

I wasn't sure where to put this, since I only see the omap-image-builder thing and this is not omap-specific. Anyway, using the debian/ubuntu minfs on chromebooks requires the rfkill tool to release the soft blocks on wifi/bt before they can be configured (I'm not sure if this issue comes up on any other platforms or not). I hacked up a chromebook script to use your minfs tarballs and the only real issue is installing rfkill over wifi when you don't have wifi up yet ;)