i8k: Integrate with the hwmon subsystem

Let i8k create an hwmon class device so that libsensors will expose
the CPU temperature and fan speeds to monitoring applications.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Guenter Roeck <guenter.roeck@ericsson.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Massimo Dal Zotto <dz@debian.org>