net/mlx5: E-switch, Introduce rate limiting groups API

Extend eswitch API with rate limiting groups:

- Define new struct mlx5_esw_rate_group that is used to hold all
  internal group data.

- Implement functions that allow creation, destruction and cleanup of
  groups.

- Assign all vports to internal unlimited zero group by default.

This commit lays the groundwork for group rate limiting by implementing
devlink_ops->rate_node_{new|del}() callbacks to support creating and
deleting groups through devlink rate node objects. APIs that allows
setting rates and adding/removing members are implemented in following
patches.

Co-developed-by: Vlad Buslov <vladbu@nvidia.com>
Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
Signed-off-by: Dmytro Linkin <dlinkin@nvidia.com>
Reviewed-by: Huy Nguyen <huyn@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Reviewed-by: Parav Pandit <parav@nvidia.com>
Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>