We are good enough to boot upstream Linux kernels / Fedora 26/27. That
should be sufficient for now.

As the QEMU CPU model is migration safe, let's add compatibility code.
Generate the feature list to reduce the chance of messing things up in the
future.
Signed-off-by: NDavid Hildenbrand <david@redhat.com>
Message-Id: <20171208165529.14124-1-david@redhat.com>
[CH: squashed 's390x/cpumodel: make qemu cpu model play with "none" machine'
(20171213132407.5227-1-david@redhat.com) and 's390x/tcg: don't include z13
features in the qemu model' (20171213171512.17601-1-david@redhat.com) into
patch]
Signed-off-by: NCornelia Huck <cohuck@redhat.com>