[S390] Minor fault path optimization.
The minor fault path has grown a lot in terms of cycles. In particular the kprobes hook is very costly. Optimize the path to save a couple of cycles. If kprobes is enabled more than 300 cycles can be avoided if kprobes_running() is false. Signed-off-by: Martin Schwidefsky <email@example.com> Signed-off-by: Heiko Carstens <firstname.lastname@example.org>