iio: cros_ec: Add calibscale for 3d MEMS

Add calibration scale support to accel, gyro and magnetometer.

Check on eve with current firmware, check reading calibscale returns 1.0,
check with newer firmware values are applied.

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