[S390] cio: introduce purge function for /proc/cio_ignore

Allow users to remove blacklisted ccw devices by using the
/proc/cio_ignore interface:

  echo purge > /proc/cio_ignore

will remove all devices which are offline and blacklisted.

Signed-off-by: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/drivers/s390/cio/device.h b/drivers/s390/cio/device.h
index 6f5c3f2..104ed66 100644
--- a/drivers/s390/cio/device.h
+++ b/drivers/s390/cio/device.h
@@ -86,6 +86,7 @@
 int ccw_device_recognition(struct ccw_device *);
 int ccw_device_online(struct ccw_device *);
 int ccw_device_offline(struct ccw_device *);
+int ccw_purge_blacklisted(void);
 
 /* Function prototypes for device status and basic sense stuff. */
 void ccw_device_accumulate_irb(struct ccw_device *, struct irb *);