net/mlx5: Add devlink flow_steering_mode parameter

Add new parameter (flow_steering_mode) to control the flow steering
mode of the driver.
Two modes are supported:
1. DMFS - Device managed flow steering
2. SMFS - Software/Driver managed flow steering.

In the DMFS mode, the HW steering entities are created through the
FW. In the SMFS mode this entities are created though the driver
directly.

The driver will use the devlink steering mode only if the steering
domain supports it, for now SMFS will manages only the switchdev eswitch
steering domain.

User command examples:
- Set SMFS flow steering mode::

    $ devlink dev param set pci/0000:06:00.0 name flow_steering_mode value "smfs" cmode runtime

- Read device flow steering mode::

    $ devlink dev param show pci/0000:06:00.0 name flow_steering_mode
      pci/0000:06:00.0:
      name flow_steering_mode type driver-specific
      values:
         cmode runtime value smfs

Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>