net/mlx5: Maintain fs_id xarray per MACsec device inside macsec steering

Remove fs_id from the MACsec SA, since it has no real usage there and
instead maintain with the MACsec steering data inside the core.

Downstream patches requires this change to facilitate IB driver accesses
to the fs_ids to avoid RoCE MACsec dependency on EN driver.

Signed-off-by: Patrisious Haddad <phaddad@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>