hwmon: (gpio-fan) Add regulator support

hwmon: (gpio-fan) Add regulator support

FANs might be supplied by a regulator which needs to be enabled as well.
This is implemented using runtime PM. Every time speed_index changes from
0 to non-zero and vise versa RPM is resumed or suspended.
Intitial RPM state is determined by initial value of speed_index.

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Link: https://lore.kernel.org/r/20250409065430.1413439-1-alexander.stein@ew.tq-group.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>