Add linux-firmware to the set of packages we build (#6)

linux-firmware contains firmware files necessary for some devices to work.
This adds the latest linux-firmware containing bnx2x-e2-7.13.1.0.fw necessary
to Shiner-SR.

TODO(maurosr): I couldn't find the url to download Source1: cxgb4-old-fw.tar.bz2
so let's keep it out of our package for now as mentioned in linux-firmware's spec.

Added Conflicts tag against ivtv-firmware (a TV recorder device) Since we don't
care with the kind of device ivtv brings to the table (no offense, it's just not
part of our scope) I'll mark as conflict instead of repackaging and rebuild it.
see discussion at ttps://github.com//pull/6/files#r76001916

Closes #25