s390x/ap: base Adjunct Processor (AP) object model

Introduces the base object model for virtualizing AP devices.

Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
Tested-by: Pierre Morel <pmorel@linux.ibm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Message-Id: <20181010170309.12045-5-akrowiak@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>