s390x: wire up sclp console output

Now the basics should be working and therefore the self test should
pass.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20170522085702.17856-6-david@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>