padata: Convert to hotplug state machine

Install the callbacks via the state machine. CPU-hotplug multinstance support
is used with the nocalls() version. Maybe parts of padata_alloc() could be
moved into the online callback so that we could invoke ->startup callback for
instance and drop get_online_cpus().

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-crypto@vger.kernel.org
Cc: rt@linutronix.de
Link: http://lkml.kernel.org/r/20160906170457.32393-14-bigeasy@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/include/linux/padata.h b/include/linux/padata.h
index 113ee62..0f9e567 100644
--- a/include/linux/padata.h
+++ b/include/linux/padata.h
@@ -151,7 +151,7 @@
  * @flags: padata flags.
  */
 struct padata_instance {
-	struct notifier_block		 cpu_notifier;
+	struct hlist_node		 node;
 	struct workqueue_struct		*wq;
 	struct parallel_data		*pd;
 	struct padata_cpumask		cpumask;