arm/bL_switcher: Convert to hotplug state machine

Install the callbacks via the state machine.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: rt@linuxtronix.de
Cc: linux-arm-kernel@lists.infradead.org
Cc: Russell King <linux@armlinux.org.uk>
Link: http://lkml.kernel.org/r/20161117183541.8588-15-bigeasy@linutronix.de


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