media: dt-bindings: alvium: add document YAML binding

Add documentation of device tree in YAML schema for the ALVIUM
Camera from Allied Vision Inc.

References:
 - https://www.alliedvision.com/en/products/embedded-vision-solutionsSigned-off-by: Tommaso Merciai <tomm.merciai@gmail.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>

Documentation/devicetree/bindings/media/i2c/alliedvision,alvium-csi2.yaml

+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/media/i2c/alliedvision,alvium-csi2.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Allied Vision Alvium Camera
+
+maintainers:
+  - Tommaso Merciai <tomm.merciai@gmail.com>
+  - Martin Hecht <martin.hecht@avnet.eu>
+
+allOf:
+  - $ref: /schemas/media/video-interface-devices.yaml#
+
+properties:
+  compatible:
+    const: alliedvision,alvium-csi2
+
+  reg:
+    maxItems: 1
+
+  vcc-ext-in-supply:
+    description: |
+      The regulator that supplies power to the VCC_EXT_IN pins.
+
+  port:
+    description: Digital Output Port
+    $ref: /schemas/graph.yaml#/$defs/port-base
+    additionalProperties: false
+
+    properties:
+      endpoint:
+        $ref: /schemas/media/video-interfaces.yaml#
+        unevaluatedProperties: false
+
+        properties:
+          link-frequencies: true
+
+          data-lanes:
+            minItems: 1
+            items:
+              - const: 1
+              - const: 2
+              - const: 3
+              - const: 4
+
+        required:
+          - data-lanes
+          - link-frequencies
+
+required:
+  - compatible
+  - reg
+  - vcc-ext-in-supply
+  - port
+
+additionalProperties: false
+
+examples:
+  - |
+    i2c {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        alvium: camera@3c {
+            compatible = "alliedvision,alvium-csi2";
+            reg = <0x3c>;
+            vcc-ext-in-supply = <&reg_vcc_ext_in>;
+
+            port {
+                alvium_out: endpoint {
+                    remote-endpoint = <&mipi_csi_0_in>;
+                    data-lanes = <1 2 3 4>;
+                    link-frequencies = /bits/ 64 <681250000>;
+                };
+            };
+        };
+    };
+
+...