dt-bindings: sun6i-dsi: Add VCC-DSI supply property

Allwinner MIPI DSI controllers are supplied with SoC DSI
power rails via VCC-DSI pin.

Some board still work without supplying this but give more
faith on datasheet and hardware schematics and document this
supply property in required property list.
Reviewed-by: Rob Herring <robh@kernel.org>
Tested-by: Merlijn Wajer <merlijn@wizzup.org>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191003064527.15128-5-jagan@amarulasolutions.com

Documentation/devicetree/bindings/display/allwinner,sun6i-a31-mipi-dsi.yaml

@@ -36,6 +36,9 @@ properties:
   resets:
     maxItems: 1
 
+  vcc-dsi-supply:
+    description: VCC-DSI power supply of the DSI encoder
+
   phys:
     maxItems: 1
 
@@ -64,6 +67,7 @@ required:
   - phys
   - phy-names
   - resets
+  - vcc-dsi-supply
   - port
 
 additionalProperties: false
@@ -79,6 +83,7 @@ examples:
         resets = <&ccu 4>;
         phys = <&dphy0>;
         phy-names = "dphy";
+        vcc-dsi-supply = <&reg_dcdc1>;
         #address-cells = <1>;
         #size-cells = <0>;