mlxsw: reg: Add Port Module To local DataBase Register

The PMTDB register allows to query the possible module<->local port
mapping than can be used in PMLP. It does not represent the actual/current
mapping of the local to module. Actual mapping is only defined by PMLP.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>