mlxsw: reg: Add Port Local port to Label Port mapping Register

The PLLP register returns the mapping from Local Port into Label Port.

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>