Build a separate package for faup1090.

This sorts out a few dependency problems:
1) we want to build faup1090 for use by piaware, but don't want to require that fadump1090 is installed to use piaware;
1a) in particular merely installing piaware/faup1090 should not cause fadump1090 to try to start on boot
2) faup1090 doesn't need a dependency on librtlsdr

This should satisfy these usecases:

* Nothing already installed: install librtlsdr0, fadump1090, faup1090, piaware
  (Or just "piaware" + "fadump1090" once there's a proper repository)

* Already have a dump1090 running: install faup1090, piaware
  (Or just "piaware" once there's a proper repository)