hwmon: (core) Add support for pwm auto channels attribute

pwm[1-*]_auto_channels_temp is documented as an official
hwmon sysfs attribute, yet there is no support for it in
the new with_info-API. Fix that.

Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://lore.kernel.org/r/20220224061210.16452-2-W_Armin@gmx.de
Signed-off-by: Guenter Roeck <linux@roeck-us.net>