s390x: Fixup interrupt psws

Let's use the svc psw instead of the mcck psw for svc interrupts
and name it supervisor call. Also we exchange the io int psw for the
right one.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>