net/mlx5e: Add devlink fdb_large_groups parameter

Add a devlink parameter to control the number of large groups in a
autogrouped flow table. The default value is 15, and the range is between 1
and 1024.

The size of each large group can be calculated according to the following
formula: size = 4M / (fdb_large_groups + 1).

Examples:
- Set the number of large groups to 20.
    $ devlink dev param set pci/0000:82:00.0 name fdb_large_groups \
      cmode driverinit value 20

  Then run devlink reload command to apply the new value.
    $ devlink dev reload pci/0000:82:00.0

- Read the number of large groups in flow table.
    $ devlink dev param show pci/0000:82:00.0 name fdb_large_groups
    pci/0000:82:00.0:
      name fdb_large_groups type driver-specific
        values:
          cmode driverinit value 20

Signed-off-by: Jianbo Liu <jianbol@mellanox.com>
Reviewed-by: Vlad Buslov <vladbu@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>