iio: cros_ec: Add sign vector in core for backward compatibility

iio: cros_ec: Add sign vector in core for backward compatibility

To allow cros_ec iio core library to be used with legacy device, add a
vector to rotate sensor data if necessary: legacy devices are not
reporting data in HTML5/Android sensor referential.

Check the data is not rotated on recent chromebooks that use the HTML5
standard to present sensor data.

Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>