s390x/tcg: wire up STORE CHANNEL REPORT WORD

CRW machine check handling requires STCRW. So let's wire it up.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20171208160207.26494-6-david@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
