apm821xx: tc654: add driver for Microchip TC654/TC655 PWM fan controllers

apm821xx: tc654: add driver for Microchip TC654/TC655 PWM fan controllers

This patch adds a hwmon driver for the Microchip TC654 and TC655
Dual SMBus PWM Fan Speed Controllers with Fan Fault detection.

The chip is described in the DS2001734C Spec Document from Microchip.
It supports:
	- Shared PWM Fan Drive for two fans
	- Provides RPM
	- automatic PWM controller (needs additional
	  NTC/PTC Thermistors.)
	- Overtemperature alarm (when using NTC/PTC
	  Thermistors)

The TC654 is used by the Netgear WNDR47X0 to control its
system fan.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>