dt-bindings: ipmi: Convert IPMI-SMIC bindings to json-schema

Convert the generic IPMI controller bindings to DT schema format
using json-schema.

The device_type property is deprecated for most node per the DT spec,
but at least the Linux driver matches on it, so I keep it in.

The Linux driver parses for some additional and optional properties,
but there are no in-tree users. Let's allow extra properties to cover
any other users.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/ipmi/ipmi-smic.txt

-IPMI device
-
-Required properties:
-- compatible: should be one of ipmi-kcs, ipmi-smic, or ipmi-bt
-- device_type: should be ipmi
-- reg: Address and length of the register set for the device
-
-Optional properties:
-- interrupts: The interrupt for the device.  Without this the interface
-	is polled.
-- reg-size - The size of the register.  Defaults to 1
-- reg-spacing - The number of bytes between register starts.  Defaults to 1
-- reg-shift - The amount to shift the registers to the right to get the data
-	into bit zero.
-
-Example:
-
-smic@fff3a000 {
-	compatible = "ipmi-smic";
-	device_type = "ipmi";
-	reg = <0xfff3a000 0x1000>;
-	interrupts = <0 24 4>;
-	reg-size = <4>;
-	reg-spacing = <4>;
-};

Documentation/devicetree/bindings/ipmi/ipmi-smic.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/ipmi/ipmi-smic.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: IPMI device bindings
+
+description: IPMI device bindings
+
+maintainers:
+  - Corey Minyard <cminyard@mvista.com>
+
+properties:
+  compatible:
+    enum:
+      - ipmi-kcs
+      - ipmi-smic
+      - ipmi-bt
+
+  device_type:
+    items:
+      - const: "ipmi"
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    description: Interface is polled if this property is omitted.
+    maxItems: 1
+
+  reg-size:
+    description: The access width of the register in bytes. Defaults to 1.
+    allOf:
+      - $ref: /schemas/types.yaml#/definitions/uint32
+      - enum: [1, 2, 4, 8]
+
+  reg-spacing:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description: The number of bytes between register starts. Defaults to 1.
+
+  reg-shift:
+    description: |
+      The amount of bits to shift the register content to the right to get
+      the data into bit zero.
+    allOf:
+      - $ref: /schemas/types.yaml#/definitions/uint32
+      - maximum: 56
+
+required:
+  - compatible
+  - reg
+
+examples:
+  - |
+    smic@fff3a000 {
+        compatible = "ipmi-smic";
+        device_type = "ipmi";
+        reg = <0xfff3a000 0x1000>;
+        interrupts = <0 24 4>;
+        reg-size = <4>;
+        reg-spacing = <4>;
+    };