[S390] cio: Update documentation.

- read_dev_chars()/read_conf_data() are deprecated. Don't document them, but
  advise to issue the channel program from the driver itself.
- Remove some really obsolete and incorrect stuff.

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>