net/mlx5: Move chains ft pool to be used by all firmware steering

Firmware FT pool is per device, but the software tracking of this pool
only services fs_chains users, and if another layer takes a flow table,
the pool will not be updated, and fs_chains will fail creating a flow
table, with no recovery till the flow table is returned.

Move FT pool to be global per device, and stored at the cmd level,
so all layers can use it.

Signed-off-by: Paul Blakey <paulb@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>