dt-bindings: clock: mediatek: convert SSUSBSYS to the json-schema clock

This helps validating DTS files. Introduced changes:
1. Documented "reg" property
2. Dropped "syscon" as it was incorrectly used
3. Adjusted nodename, "compatible" and "reg" in example

Signed-off-by: Rafał Miłecki <[e-mail]>
Reviewed-by: Krzysztof Kozlowski <[e-mail]>
Reviewed-by: AngeloGioacchino Del Regno <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Stephen Boyd <[e-mail]>

Documentation/devicetree/bindings/arm/mediatek/mediatek,ssusbsys.txt

···
-MediaTek SSUSBSYS controller
-============================
-
-The MediaTek SSUSBSYS controller provides various clocks to the system.
-
-Required Properties:
-
-- compatible: Should be:
-	- "mediatek,mt7622-ssusbsys", "syscon"
-	- "mediatek,mt7629-ssusbsys", "syscon"
-- #clock-cells: Must be 1
-- #reset-cells: Must be 1
-
-The SSUSBSYS controller uses the common clk binding from
-Documentation/devicetree/bindings/clock/clock-bindings.txt
-The available clocks are defined in dt-bindings/clock/mt*-clk.h.
-
-Example:
-
-ssusbsys: ssusbsys@1a000000 {
-	compatible = "mediatek,mt7622-ssusbsys", "syscon";
-	reg = <0 0x1a000000 0 0x1000>;
-	#clock-cells = <1>;
-	#reset-cells = <1>;
-};

Documentation/devicetree/bindings/clock/mediatek,mt7622-ssusbsys.yaml

···
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/clock/mediatek,mt7622-ssusbsys.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: MediaTek SSUSBSYS clock and reset controller
+
+description:
+  The MediaTek SSUSBSYS controller provides various clocks to the system.
+
+maintainers:
+  - Matthias Brugger <[e-mail]>
+
+properties:
+  compatible:
+    enum:
+      - mediatek,mt7622-ssusbsys
+      - mediatek,mt7629-ssusbsys
+
+  reg:
+    maxItems: 1
+
+  "#clock-cells":
+    const: 1
+    description: The available clocks are defined in dt-bindings/clock/mt*-clk.h
+
+  "#reset-cells":
+    const: 1
+
+required:
+  - reg
+  - "#clock-cells"
+  - "#reset-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    clock-controller@1a000000 {
+        compatible = "mediatek,mt7622-ssusbsys";
+        reg = <0x1a000000 0x1000>;
+        #clock-cells = <1>;
+        #reset-cells = <1>;
+    };