s390x: Move typedef SCLPEventFacility to event-facility.h

s390x: Move typedef SCLPEventFacility to event-facility.h

This will make future conversion to OBJECT_DECLARE* easier.

In sclp.h, use "struct SCLPEventFacility" to avoid introducing
unnecessary header dependencies.

Acked-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Tested-By: Roman Bolshakov <r.bolshakov@yadro.com>
Message-Id: <20200825192110.3528606-29-ehabkost@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>