hwmon: (coretemp) Convert to hotplug state machine

Install the callbacks via the state machine. Setup and teardown are handled
by the hotplug core.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-hwmon@vger.kernel.org
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Jean Delvare <jdelvare@suse.com>
Cc: rt@linuxtronix.de
Cc: Guenter Roeck <linux@roeck-us.net>
Link: http://lkml.kernel.org/r/20161117183541.8588-5-bigeasy@linutronix.de


Signed-off-by: Guenter Roeck <linux@roeck-us.net>