s390x/tcg: make testblock use the new _real mmu

Low address protection checks will be moved into the mmu later.

Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20170926183318.12995-6-david@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
