[S390] get rid of kprobes notifier call chain.

And here's a port of the powerpc patch to get rid of the notifier
chain completely to s390.  It's ontop of Martins patch as that one
is in mainline already.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>