s390x/tcg: cleanup service interrupt injection

There are still some leftovers from old virtio interrupts in there.
Most importantly, we don't have to queue service interrupts anymore.
Just like KVM, we can simply multiplex the SCLP service interrupts and
avoid the queue.

Also, now only valid parameters/cpu_addr will be stored on service
interrupts.

Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20170928203708.9376-3-david@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
