dt-bindings: altera: Convert clkmgr binding to json-schema

Convert Altera clkmgr to DT schema format using json-schema.

Cc: Mark Rutland <mark.rutland@arm.com>
Acked-by: Dinh Nguyen <dinguyen@kernel.org>
Cc: devicetree@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/arm/altera/socfpga-clk-manager.txt

-Altera SOCFPGA Clock Manager
-
-Required properties:
-- compatible : "altr,clk-mgr"
-- reg : Should contain base address and length for Clock Manager
-
-Example:
-	 clkmgr@ffd04000 {
-		compatible = "altr,clk-mgr";
-		reg = <0xffd04000 0x1000>;
-	};

Documentation/devicetree/bindings/arm/altera/socfpga-clk-manager.yaml

+# SPDX-License-Identifier: GPL-2.0
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/arm/altera/socfpga-clk-manager.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Altera SOCFPGA Clock Manager
+
+maintainers:
+  - Dinh Nguyen <dinguyen@kernel.org>
+
+description: test
+
+properties:
+  compatible:
+    items:
+      - const: altr,clk-mgr
+  reg:
+    maxItems: 1
+
+required:
+  - compatible
+
+examples:
+  - |
+    clkmgr@ffd04000 {
+      compatible = "altr,clk-mgr";
+      reg = <0xffd04000 0x1000>;
+    };
+
+...