dt-bindings: iio: accel: mma8452: add power supplies property

The accelerometer's power supplies could be controllable on some
platforms, add property "vdd/vddio" power supply to let device tree
to pass phandles to the regulators to driver.
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/accel/mma8452.txt

@@ -20,6 +20,10 @@ Optional properties:
   - interrupt-names: should contain "INT1" and/or "INT2", the accelerometer's
 		     interrupt line in use.
 
+  - vdd-supply: phandle to the regulator that provides vdd power to the accelerometer.
+
+  - vddio-supply: phandle to the regulator that provides vddio power to the accelerometer.
+
 Example:
 
 	mma8453fc@1d {