s390/cio: add condev keyword to cio_ignore

Provide a 'condev' keyword to cio_ignore to (un)ignore the
CCW console device.

Reviewed-by: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>
Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>