net/mlx5: E-Switch, Add chains and priorities

A chain is a group of priorities, so use the fdb parallel
sub namespaces to implement chains, and a flow table for each
priority in them.

Because these namespaces are parallel and in series to the slow path
fdb, the chains aren't connected to one another (but to the slow path),
and one must use a explicit goto action to reach a different chain.

Flow tables for the priorities will be created on demand and destroyed
once not used.

The Firmware has four pools of tables for sizes S/XS/M/L (4k, 64k, 1m, 4m).
We maintain ghost copies of the pools occupancy.

When a new table is to be created, we scan the pools from large to small
and find the 1st table size which can be now created. When a table is
destroyed, we update the relevant pool.

Multi chain/prio isn't enabled yet by this patch, for now all flows
will use the default chain 0, and prio 1.

Signed-off-by: Paul Blakey <paulb@mellanox.com>
Reviewed-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>