add ppc64le and s390x
I believe the current pungi compose config specifies just aarch64 and x86_64 primarily for the historical reason that it was inherited from Fedora IoT which only targets those architectures. It is a toplevel goal of this project that it is Fedora and works everywhere that dnf does, which includes ppc64le and s390x.
I believe we can just add those to the pungi config.
The base image builds locally here, though for some reason we're missing zipl...that needs debugging.