media: dt-bindings: i2c: Add I2C Address Translator (ATR)

Add bindings for I2C Address Translator. Only one property is added,
'i2c-alias-pool', which can be used in the bindings for the device that
supports ATR.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Acked-by: Wolfram Sang <wsa@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

Documentation/devicetree/bindings/i2c/i2c-atr.yaml

+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/i2c/i2c-atr.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Common i2c address translator properties
+
+maintainers:
+  - Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
+
+description:
+  An I2C Address Translator (ATR) is a device with an I2C slave parent
+  ("upstream") port and N I2C master child ("downstream") ports, and
+  forwards transactions from upstream to the appropriate downstream port
+  with a modified slave address. The address used on the parent bus is
+  called the "alias" and is (potentially) different from the physical
+  slave address of the child bus. Address translation is done by the
+  hardware.
+
+properties:
+  i2c-alias-pool:
+    $ref: /schemas/types.yaml#/definitions/uint32-array
+    description:
+      I2C alias pool is a pool of I2C addresses on the main I2C bus that can be
+      used to access the remote peripherals on the serializer's I2C bus. The
+      addresses must be available, not used by any other peripheral. Each
+      remote peripheral is assigned an alias from the pool, and transactions to
+      that address will be forwarded to the remote peripheral, with the address
+      translated to the remote peripheral's real address. This property is not
+      needed if there are no I2C addressable remote peripherals.
+
+additionalProperties: true
+...