Package virtio-bindings

This is my first try ever with a rust crate in Debian. Haven't done an ./release.sh / upload because I want some review first.

The virtio-binding crate is a prerequisite for another package I'm working on (libblkio), along with a few other crates currently missing in debian.

This one has some rough corners still, due to bindgen issues, which were fixed in later commits but there was no release yet. I thought I'd package actual release together with the issues first, especially since I know it actually works.

Also, it might be better to remove the auto-generated bindings files entirely, and run bindgen in d/rules directly, than to ship bindgen-generated files in the source. But again, this is what the upstream has now. It is not exactly clear what license to use for those bindgen-generated files though.