net/mlx5: Instantiate separate mapping objects for FDB and NIC tables

Currently, the u32 chain id is mapped to u16 value which is stored on
the lower 16 bits of reg_c0 for FDB and reg_b for NIC tables. The
mapping is internally maintained by the chains object. However, with
the introduction of reg_c0 objects the fdb may store more than just
the chain id on reg_c0. This is not relevant for NIC tables.

Separate the chains mapping instantiation for FDB and NIC tables.
Remove the mapping from the chains object. For FDB tables, create
the mapping per eswitch. For NIC tables, create the mapping per tc
table. Pass the corresponding mapping pointer when creating the
chains object.

Signed-off-by: Chris Mi <cmi@nvidia.com>
Reviewed-by: Oz Shlomo <ozsh@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>