s390x/tcg: implement SIGP CONDITIONAL EMERGENCY SIGNAL

Mostly analogous to the kernel/KVM version (so I assume the checks are
correct :) ). As a preparation for TCG.

Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20170928203708.9376-24-david@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
