net/mlx5: fs_core: Introduce unmanaged flow tables

Currently, Most of the steering tree is statically declared ahead of time,
with steering prios instances allocated for each fdb chain to assign max
number of levels for each of them. This allows fs_core to manage the
connections and  levels of the flow tables hierarcy to prevent loops, but
restricts us with the number of supported chains and priorities.

Introduce unmananged flow tables, allowing the user to manage the flow
table connections. A unamanged table is detached from the fs_core flow
table hierarcy, and is only connected back to the hierarchy by explicit
FTEs forward actions.

This will be used together with firmware that supports ignoring the flow
table levels to increase the number of supported chains and prios.

Signed-off-by: Paul Blakey <paulb@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Reviewed-by: Oz Shlomo <ozsh@mellanox.com>
Reviewed-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>