Formalize how the xc3sprog flash burning tools get installed.

The FPGA images are burnt using the open-source xc3sprog tools. We should formalize how those get installed. At JHU I built and installed them into a eups product. There is no standard xc3sprog apt package, so that's probably the right thing to do. But would like to be able to do a pfsinstall xc3sprog:whatever.