travis.yml: Add the selftest-setup ppc64 test

This test now seems to be working with the newer version of QEMU in
Ubuntu Focal, so we can run it now in the Travis builds, too.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20201001072234.143703-4-thuth@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>