[S390] Some preparations for the dynamic subchannel mapping patch.

- Move adding subchannel attributes to css_register_subchannel().
- Don't call device_trigger_reprobe() for non-operational devices.
- Introduce io_subchannel_create_ccwdev().

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>