hwmon: (pmbus/cffps) Add led class device for power supply fault led

This power supply device doesn't correctly manage it's own fault led.
Add an led class device and register it so that userspace can manage
power supply fault led as necessary.

Signed-off-by: Eddie James <eajames@linux.vnet.ibm.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>