devlink: add documentation for ionic device driver

The IONIC device driver allocates a devlink and reports versions. Add
documentation for this driver.
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Cc: Shannon Nelson <snelson@pensando.io>
Acked-by: Shannon Nelson <snelson@pensandi.io>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/devlink/index.rst

@@ -30,6 +30,7 @@ parameters, info versions, and other features it supports.
    :maxdepth: 1
 
    bnxt
+   ionic
    mlx4
    mlx5
    mlxsw

Documentation/networking/devlink/ionic.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+=====================
+ionic devlink support
+=====================
+
+This document describes the devlink features implemented by the ``ionic``
+device driver.
+
+Info versions
+=============
+
+The ``ionic`` driver reports the following versions
+
+.. list-table:: devlink info versions implemented
+   :widths: 5 5 90
+
+   * - Name
+     - Type
+     - Description
+   * - ``fw``
+     - running
+     - Version of firmware running on the device
+   * - ``asic.id``
+     - fixed
+     - The ASIC type for this device
+   * - ``asic.rev``
+     - fixed
+     - The revision of the ASIC for this device