hwmon: (nct6775) Add support for automatic fan control

        * 0 DC output

        * 1 PWM output

Common fan control attributes

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pwm[1-5]_temp_sel	Temperature source. Value is temperature sensor index.

			For example, select '1' for temp1_input.

Thermal Cruise mode (2)

-----------------------

If the temperature is in the range defined by:

pwm[1-5]_target_temp	Target temperature, unit millidegree Celsius

			(range 0 - 127000)

pwm[1-5]_temp_tolerance

			Target temperature tolerance, unit millidegree Celsius

there are no changes to fan speed. Once the temperature leaves the interval, fan

speed increases (if temperature is higher that desired) or decreases (if

temperature is lower than desired), using the following limits and time

intervals.

pwm[1-5]_start		fan pwm start value (range 1 - 255), to start fan

			when the temperature is above defined range.

pwm[1-5]_floor		lowest fan pwm (range 0 - 255) if temperature is below

			the defined range. If set to 0, the fan is expected to

			stop if the temperature is below the defined range.

pwm[1-5]_step_up_time	milliseconds before fan speed is increased

pwm[1-5]_step_down_time	milliseconds before fan speed is decreased

pwm[1-5]_stop_time	how many milliseconds must elapse to switch

			corresponding fan off (when the temperature was below

			defined range).

Speed Cruise mode (3)

---------------------

This modes tries to keep the fan speed constant.

fan[1-5]_target		Target fan speed

fan[1-5]_tolerance

			Target speed tolerance

Untested; use at your own risk.

Smart Fan IV mode (5)

---------------------

This mode offers multiple slopes to control the fan speed. The slopes can be

controlled by setting the pwm and temperature attributes. When the temperature

rises, the chip will calculate the DC/PWM output based on the current slope.

There are up to seven data points depending on the chip type. Subsequent data

points should be set to higher temperatures and higher pwm values to achieve

higher fan speeds with increasing temperature. The last data point reflects

critical temperature mode, in which the fans should run at full speed.

pwm[1-5]_auto_point[1-7]_pwm

			pwm value to be set if temperature reaches matching

			temperature range.

pwm[1-5]_auto_point[1-7]_temp

			Temperature over which the matching pwm is enabled.

pwm[1-5]_temp_tolerance

			Temperature tolerance, unit millidegree Celsius

pwm[1-5]_crit_temp_tolerance

			Temperature tolerance for critical temperature,

			unit millidegree Celsius

pwm[1-5]_step_up_time	milliseconds before fan speed is increased

pwm[1-5]_step_down_time	milliseconds before fan speed is decreased

Usage Notes

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