iio: cros_ec: Add lid angle driver

Add a IIO driver that reports the angle between the lid and the base for
ChromeOS convertible device.

Tested on eve with ToT EC firmware.
Check driver is loaded and lid angle is correct.

Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>