dt-bindings: iio: gyroscope: bmg160: Document regulator supplies

BMG160 needs VDD and VDDIO regulators that might need to be explicitly
enabled. Document support for vdd/vddio-supply to implement this.
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201211183815.51269-1-stephan@gerhold.netSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/gyroscope/bosch,bmg160.yaml

@@ -19,6 +19,9 @@ properties:
   reg:
     maxItems: 1
 
+  vdd-supply: true
+  vddio-supply: true
+
   interrupts:
     minItems: 1
     description: