dt-bindings: iio: accel: kxcjk1013: Document regulator supplies

kxcjk1013 devices have VDD and VDDIO power lines. Need
to make sure the regulators are enabled before any
communication with kxcjk1013. Document support for
vdd/vddio-supply to implement this.

Signed-off-by: Devajith V S <devajithvs@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201213172437.2779-1-devajithvs@gmail.com


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