dt-bindings: connector: usb: allow a single HS port

Allow a single HS port to be used e.g. without reg property and a unit
address. OF graph allows a single port node, without 'reg' property.

This removes a couple of Warnings or errors on STM32MP boards.
When using single HS port currently, when doing building with W=1:
arch/arm/boot/dts/stm32mp157c-dk2.dtb: stusb1600@28: connector:
Unevaluated properties are not allowed ('port' was unexpected)

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Link: https://lore.kernel.org/r/20230620085633.533187-1-fabrice.gasnier@foss.st.com
Signed-off-by: Rob Herring <robh@kernel.org>

Author: Fabrice Gasnier

Documentation/devicetree/bindings/connector/usb-connector.yaml

@@ -168,6 +168,13 @@ properties:
       offer the power, Capability Mismatch is set. Required for power sink and
       power dual role.
 
+  port:
+    $ref: /schemas/graph.yaml#/properties/port
+    description: OF graph bindings modeling a data bus to the connector, e.g.
+      there is a single High Speed (HS) port present in this connector. If there
+      is more than one bus (several port, with 'reg' property), they can be grouped
+      under 'ports'.
+
   ports:
     $ref: /schemas/graph.yaml#/properties/ports
     description: OF graph bindings modeling any data bus to the connector
@@ -322,6 +329,19 @@ examples:
         };
     };
 
+  # USB-C connector attached to SoC with a single High-Speed controller
+  - |
+    connector {
+        compatible = "usb-c-connector";
+        label = "USB-C";
+
+        port {
+            high_speed_ep: endpoint {
+                remote-endpoint = <&usb_hs_ep>;
+            };
+        };
+    };
+
   # USB-C connector attached to SoC and USB3 typec port controller(hd3ss3220)
   # with SS 2:1 MUX. HS lines routed to SoC, SS lines routed to the MUX and
   # the output of MUX is connected to the SoC.