staging/lustre/libcfs: Convert to hotplug state machine

Install the callbacks via the state machine. No functional change.

Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: devel@driverdev.osuosl.org
Cc: Andreas Dilger <andreas.dilger@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Oleg Drokin <oleg.drokin@intel.com>
Cc: rt@linutronix.de
Cc: lustre-devel@lists.lustre.org
Link: http://lkml.kernel.org/r/20161202110027.htzzeervzkoc4muv@linutronix.de
Link: http://lkml.kernel.org/r/20161221192111.922872524@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>