cpuidle/powernv: Convert to hotplug state machine

Install the callbacks via the state machine.

v1…v2: - Use only CPUHP_CPUIDLE_DEAD (requested by Daniel Lezcano)

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-pm@vger.kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: rt@linutronix.de
Link: http://lkml.kernel.org/r/20160824091259.ozyslcopxvbfdqzy@linutronix.de


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>