mlxsw: switchx2: Add Infiniband switch partition

In order to put a port in Infiniband fabric it should be assigned
to separate swid (Switch partition) that initialized as IB swid.

Signed-off-by: Elad Raz <eladr@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>