KVM: s390: Add SIGP store-status-at-address order

The STORE STATUS AT ADDRESS order of SIGP was still missing.
Now it is supported, using the common kvm_s390_store_status()
function.

Signed-off-by: Thomas Huth <thuth@linux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>