dt-bindings: memory-controllers: Convert Calxeda DDR to json-schema

Convert the Calxeda DDR memory controller binding to DT schema format
using json-schema.
Although this technically covers the whole DRAM controller, the
intention to use it only for error reporting and mapping fault addresses
to DRAM chips.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/memory-controllers/calxeda-ddr-ctrlr.txt

-Calxeda DDR memory controller
-
-Properties:
-- compatible : Should be:
-  - "calxeda,hb-ddr-ctrl" for ECX-1000
-  - "calxeda,ecx-2000-ddr-ctrl" for ECX-2000
-- reg : Address and size for DDR controller registers.
-- interrupts : Interrupt for DDR controller.
-
-Example:
-
-	memory-controller@fff00000 {
-		compatible = "calxeda,hb-ddr-ctrl";
-		reg = <0xfff00000 0x1000>;
-		interrupts = <0 91 4>;
-	};

Documentation/devicetree/bindings/memory-controllers/calxeda-ddr-ctrlr.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/memory-controllers/calxeda-ddr-ctrlr.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Calxeda DDR memory controller binding
+
+description: |
+  The Calxeda DDR memory controller is initialised and programmed by the
+  firmware, but an OS might want to read its registers for error reporting
+  purposes and to learn about the DRAM topology.
+
+maintainers:
+  - Andre Przywara <andre.przywara@arm.com>
+
+properties:
+  compatible:
+    enum:
+      - calxeda,hb-ddr-ctrl
+      - calxeda,ecx-2000-ddr-ctrl
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+  - interrupts
+
+additionalProperties: false
+
+examples:
+  - |
+    memory-controller@fff00000 {
+        compatible = "calxeda,hb-ddr-ctrl";
+        reg = <0xfff00000 0x1000>;
+        interrupts = <0 91 4>;
+    };