devlink: add parameter documentation for the mlx4 driver

The mlx5 and mlxsw drivers have driver-specific documentation for the
devlink features they support. No such file was added for mlx4.

Add a file to document the mlx4 devlink support. Initially it contains
only the devlink parameters.
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Cc: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/devlink/index.rst

@@ -29,6 +29,7 @@ parameters, info versions, and other features it supports.
    :maxdepth: 1
 
    bnxt
+   mlx4
    mlx5
    mlxsw
    mv88e6xxx

Documentation/networking/devlink/mlx4.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+====================
+mlx4 devlink support
+====================
+
+This document describes the devlink features implemented by the ``mlx4``
+device driver.
+
+Parameters
+==========
+
+.. list-table:: Generic parameters implemented
+
+   * - Name
+     - Mode
+   * - ``internal_err_reset``
+     - driverinit, runtime
+   * - ``max_macs``
+     - driverinit
+   * - ``region_snapshot_enable``
+     - driverinit, runtime
+
+The ``mlx4`` driver also implements the following driver-specific
+parameters.
+
+.. list-table:: Driver-specific parameters implemented
+   :widths: 5 5 5 85
+
+   * - Name
+     - Type
+     - Mode
+     - Description
+   * - ``enable_64b_cqe_eqe``
+     - Boolean
+     - driverinit
+     - Enable 64 byte CQEs/EQEs, if the FW supports it.
+   * - ``enable_4k_uar``
+     - Boolean
+     - driverinit
+     - Enable using the 4k UAR.
+
+The ``mlx4`` driver supports reloading via ``DEVLINK_CMD_RELOAD``