s390x/tcg: implement TEST PROTECTION

Linux uses TEST PROTECTION to sense for available memory locations.

Let's implement what we can for now (just as for the other instructions,
excluding AR mode and special protection mechanisms).

Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20171218224616.21030-2-david@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>