uml: Restore proper descriptions in make deb-pkg target

From: Ryan Anderson <ryan@michonline.com>

This pulls the description from the Debian user-mode-linux package, and
puts $version back in the appropriate places for both descriptions.

Signed-off-by: Ryan Anderson <ryan@michonline.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>