81cio_ignore: rewrite module

Rewrite cio_ignore module to rely on the dracut commandline
parameter 'rd.cio_accept', which takes a comma-separated list
of CCW IDs. Each of those IDs are being removed from the
list of devices from cio_ignore.

The default values for rd.cio_accept are taken from
/boot/zipl/active_devices.txt.

References: bnc#882685

Signed-off-by: Hannes Reinecke <hare@suse.de>