dt-bindings: display: bridge: renesas,dw-hdmi: Add resets property

The DWC HDMI blocks on R-Car and RZ/G2 SoC's use resets, so to complete
the bindings include resets property.

This also fixes the below warning when running dtbs_check:
arch/arm64/boot/dts/renesas/r8a774b1-hihope-rzg2n-rev2-ex-idk-1110wr.dtb: hdmi@fead0000: Unevaluated properties are not allowed ('resets' was unexpected)
	From schema: Documentation/devicetree/bindings/display/bridge/renesas,dw-hdmi.yaml

While at it mark resets property as required as all the DT sources
in the kernel specify resets and update the example node.
Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>

Documentation/devicetree/bindings/display/bridge/renesas,dw-hdmi.yaml

@@ -38,6 +38,9 @@ properties:
   clock-names:
     maxItems: 2
 
+  resets:
+    maxItems: 1
+
   ports:
     $ref: /schemas/graph.yaml#/properties/ports
 
@@ -67,6 +70,7 @@ required:
   - reg
   - clocks
   - clock-names
+  - resets
   - interrupts
   - ports
 
@@ -85,6 +89,7 @@ examples:
         clocks = <&cpg CPG_CORE R8A7795_CLK_S0D4>, <&cpg CPG_MOD 729>;
         clock-names = "iahb", "isfr";
         power-domains = <&sysc R8A7795_PD_ALWAYS_ON>;
+        resets = <&cpg 729>;
 
         ports {
             #address-cells = <1>;