It is probably worth spending the time to split them up with
multiple upstream tarballs, but for now, usbboot, xbboot, and so on
are in a single repository managed as a single project.
Teach debian/rules get-orig-source to build a single upstream tarball
with the entire source tree.
Include history of whole tree in the generated changelog.upstream.
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>