hwmon: (cros_ec) add PWM control over fans

hwmon: (cros_ec) add PWM control over fans

Newer EC firmware supports controlling fans through host commands, so
adding corresponding implementations for controlling these fans in the
driver for other kernel services and userspace to control them.

The driver will first probe the supported host command versions (get and
set of fan PWM values, get and set of fan control mode) to see if the
connected EC fulfills the requirements of controlling the fan, then
exposes corresponding sysfs nodes for userspace to control the fan with
corresponding read and write implementations.
As EC will automatically change the fan mode to auto when the device is
suspended, the power management hooks are added as well to keep the fan
control mode and fan PWM value consistent during suspend and resume. As
we need to access the hwmon device in the power management hook, update
the driver by storing the hwmon device in the driver data as well.

Signed-off-by: Sung-Chi Li <lschyi@chromium.org>
Acked-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/r/20250911-cros_ec_fan-v6-2-a1446cc098af@google.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>