dt-bindings: display: panel-simple-dsi: document port

Panels are supposed to have one port (coming from panel-common.yaml
binding):

  msm8916-samsung-a3u-eur.dtb: panel@0: 'port' does not match any of the regexes: 'pinctrl-[0-9]+'

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20230326155425.91181-4-krzysztof.kozlowski@linaro.org
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/display/panel/samsung,s6e88a0-ams452ef01.yaml

@@ -16,6 +16,7 @@ properties:
   compatible:
     const: samsung,s6e88a0-ams452ef01
   reg: true
+  port: true
   reset-gpios: true
   vdd3-supply:
     description: core voltage supply
@@ -25,6 +26,7 @@ properties:
 required:
   - compatible
   - reg
+  - port
   - vdd3-supply
   - vci-supply
   - reset-gpios
@@ -46,5 +48,11 @@ examples:
                     vdd3-supply = <&pm8916_l17>;
                     vci-supply = <&reg_vlcd_vci>;
                     reset-gpios = <&msmgpio 25 GPIO_ACTIVE_HIGH>;
+
+                    port {
+                            panel_in: endpoint {
+                                    remote-endpoint = <&dsi0_out>;
+                            };
+                    };
             };
     };