From: Martin Schwidefsky <schwidefsky@de.ibm.com>

Common i/o layer changes:
 - Don't use bus ids in crw debug feature.
 - Use cio_oper for oper notification to disconnected devices.
 - Remove __get_subchannel_by_stsch.
 - Make cio workqueue a single threaded workqueue.
 - Introduce addiotnal cio_notify workqueue for device driver notification.
 - Switch off path in vpm if cio_start returned -ENODEV.
 - Fix rescan for new subchannels after a logical vary on.