dt-bindings: pinctl: amlogic,pinctrl-a4: Add compatible string for S7/S7D/S6

Update dt-binding document for pinctrl of Amlogic S7/S7D/S6.

Signed-off-by: Xianwei Zhao <[e-mail]>
Reviewed-by: Krzysztof Kozlowski <[e-mail]>
Link: https://lore.kernel.org/[e-mail]
Signed-off-by: Linus Walleij <[e-mail]>

Documentation/devicetree/bindings/pinctrl/amlogic,pinctrl-a4.yaml

···
 properties:
   compatible:
     oneOf:
-      - const: amlogic,pinctrl-a4
+      - enum:
+          - amlogic,pinctrl-a4
+          - amlogic,pinctrl-s6
+          - amlogic,pinctrl-s7
       - items:
           - enum:
               - amlogic,pinctrl-a5
           - const: amlogic,pinctrl-a4
+      - items:
+          - enum:
+              - amlogic,pinctrl-s7d
+          - const: amlogic,pinctrl-s7
 
   "#address-cells":
     const: 2