hwmon: add ChromeOS EC driver

The ChromeOS Embedded Controller exposes fan speed and temperature
readings.
Expose this data through the hwmon subsystem.

The driver is designed to be probed via the cros_ec mfd device.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20240529-cros_ec-hwmon-v4-2-5cdf0c5db50a@weissschuh.net


[tzungbi: Fixed typo in MAINTAINERS: "chros_ec_hwmon" -> "cros_ec_hwmon"]
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>