hwmon: (pwm-fan) Refactor fan power on/off

In preparation for dynamically switching regulator, split the power on
and power off sequence into separate functions.

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20220914153137.613982-2-alexander.stein@ew.tq-group.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>