hwmon/f71805f: Add temperature-tracking fan control mode

Add support for the "temperature mode" fan speed control. In this mode,
the user can define 3 temperature/speed trip points, and the chip will
set the speed automatically according to the temperature changes.

Signed-off-by: Phil Endecott <kernel@chezphil.org>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Mark M. Hoffman <mhoffman@lightlink.com>