From: Christian Borntraeger <cborntra@de.ibm.com>

Debug feature changes:
 - Add system control to stop the debug feature.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>