dt-bindings: iio: imu: st_lsm6dsx: add ism330is

Add device bindings for ism330is IMU sensor.
Use lsm6dso16is as fallback device for ism330is since it implements all the
features currently supported by ism330is.

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/a7a8a00037952928364269615ee8b6da4547795b.1669279604.git.lorenzo@kernel.org


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>