dt-bindings: pinctrl: Fix node descriptions in uniphier-pinctrl example

Drop parent node of the pinctrl as it is not directly necessary, and
add more examples, that is "groups", "function", and a child node to set
pin attributes, to express this pinctrl node in detail.
Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Link: https://lore.kernel.org/r/20221213082449.2721-4-hayashi.kunihiko@socionext.comSigned-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/pinctrl/socionext,uniphier-pinctrl.yaml

 # SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+
 %YAML 1.2
 ---
 $id: http://devicetree.org/schemas/pinctrl/socionext,uniphier-pinctrl.yaml#
@@ -69,11 +70,17 @@ examples:
   - |
     // The UniPhier pinctrl should be a subnode of a "syscon" compatible node.
 
-    soc-glue@5f800000 {
-        compatible = "socionext,uniphier-pro4-soc-glue", "simple-mfd", "syscon";
-        reg = <0x5f800000 0x2000>;
+    pinctrl {
+        compatible = "socionext,uniphier-ld20-pinctrl";
+
+        pinctrl_ether_rgmii: ether-rgmii {
+            groups = "ether_rgmii";
+            function = "ether_rgmii";
 
-        pinctrl: pinctrl {
-            compatible = "socionext,uniphier-pro4-pinctrl";
+            tx {
+                pins = "RGMII_TXCLK", "RGMII_TXD0", "RGMII_TXD1",
+                       "RGMII_TXD2", "RGMII_TXD3", "RGMII_TXCTL";
+                drive-strength = <9>;
+            };
         };
     };