dt-bindings/display/panel: otm8009a: Add optional power-supply property

Some boards use a dedicated voltage regulator for this panel.
Add & document this related optional power-supply property.

Signed-off-by: Philippe Cornu <philippe.cornu@st.com>
Reviewed-by: Yannick Fertré <yannick.fertre@st.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180205094532.23547-2-philippe.cornu@st.com

Documentation/devicetree/bindings/display/panel/orisetech,otm8009a.txt

@@ -9,6 +9,7 @@ Required properties:
 
 Optional properties:
   - reset-gpios: a GPIO spec for the reset pin (active low).
+  - power-supply: phandle of the regulator that provides the supply voltage.
 
 Example:
 &dsi {
@@ -17,5 +18,6 @@ Example:
 		compatible = "orisetech,otm8009a";
 		reg = <0>;
 		reset-gpios = <&gpioh 7 GPIO_ACTIVE_LOW>;
+		power-supply = <&v1v8>;
 	};
 };