hwmon: (pwm-fan) Add dedicated power switch function

This handles enabling/disabling the regulator in a single function, while
keeping the enables/disabled balanced. This is a preparation when
regulator is switched from different code paths.

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Link: https://lore.kernel.org/r/20220914153137.613982-4-alexander.stein@ew.tq-group.com


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