dt-bindings: embedded-controller: add Traverse Ten64 board controller

Add device tree binding for the board (micro)controller on Ten64 family
boards[1].

The schema is simple and is (presently) only consumed by U-Boot, but it
is possible nvmem, watchdog and other features could be described in
the future, as well as extension to future Traverse boards.

[1] https://ten64doc.traverse.com.au/hardware/microcontroller/

Signed-off-by: Mathew McBride <[e-mail]>
Acked-by: Conor Dooley <[e-mail]>
Signed-off-by: Shawn Guo <[e-mail]>

Documentation/devicetree/bindings/embedded-controller/traverse,ten64-controller.yaml

···
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/embedded-controller/traverse,ten64-controller.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Traverse Ten64 board microcontroller
+
+maintainers:
+  - Mathew McBride <[e-mail]>
+
+description: |
+  The board microcontroller on the Ten64 board family is responsible for
+  management of power sources on the board, as well as signalling the SoC
+  to power on and reset.
+
+properties:
+  compatible:
+    const: traverse,ten64-controller
+
+  reg:
+    const: 0x7e
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    i2c {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        board-controller@7e {
+            compatible = "traverse,ten64-controller";
+            reg = <0x7e>;
+        };
+    };