iio: imu: st_lsm6dsx: configure full scale on slave device if supported

Introduce st_lsm6dsx_shub_set_full_scale routine in order to configure
the i2c slave device sensitivity

Tested-by: Jimmy Assarsson <jimmyassarsson@gmail.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>