platform/chrome: update pwm fan control host commands

Update cros_ec_commands.h to include definitions for getting PWM fan
duty, getting and setting the fan control mode.

Signed-off-by: Sung-Chi Li <lschyi@chromium.org>
Acked-by: Tzung-Bi Shih <tzungbi@kernel.org>
Reviewed-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/r/20250911-cros_ec_fan-v6-1-a1446cc098af@google.com


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