iio: cros_ec_sensors: add ChromeOS EC Contiguous Sensors driver

Handle 3d contiguous sensors like Accelerometers, Gyroscope and
Magnetometer that are presented by the ChromeOS EC Sensor hub.

Signed-off-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>