dt-bindings: iio: accel: kxcjk1013: Add device tree binding documentation

Document device tree bindings for Kionix KXCJK-1013 Accelerometer driver.

Signed-off-by: Robert Yang <decatf@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>