Make the automatic fan speed control lookup table writable. This lets
the user tweak the fan speed / temperature response curve.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Guenter Roeck <guenter.roeck@ericsson.com>
Tested-by: Guenter Roeck <guenter.roeck@ericsson.com>