dt-bindings: soc: amlogic,meson-gx-hhi-sysctrl: Document the System Control registers found on early Meson SoC

The early Amlogic SoCs also has a System Control registers register set,
document it in the amlogic,meson-gx-hhi-sysctrl now the clock controller
has been converted to yaml dt-schema.

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Link: https://lore.kernel.org/r/20241007-topic-amlogic-arm32-upstream-bindings-fixes-hhi-sysctrl-meson8-v1-1-896b24e6c3c8@linaro.org
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>

Documentation/devicetree/bindings/soc/amlogic/amlogic,meson-gx-hhi-sysctrl.yaml

@@ -13,6 +13,7 @@ properties:
   compatible:
     items:
       - enum:
+          - amlogic,meson-hhi-sysctrl
           - amlogic,meson-gx-hhi-sysctrl
           - amlogic,meson-gx-ao-sysctrl
           - amlogic,meson-axg-hhi-sysctrl
@@ -36,6 +37,19 @@ properties:
     type: object
 
 allOf:
+  - if:
+      properties:
+        compatible:
+          enum:
+            - amlogic,meson-hhi-sysctrl
+    then:
+      properties:
+        clock-controller:
+          $ref: /schemas/clock/amlogic,meson8-clkc.yaml#
+
+        pinctrl: false
+        phy: false
+
   - if:
       properties:
         compatible: