mlxsw: reg: Add Tunnel Port Configuration Register

This register enables / disables learning on different types of tunnel
ports (e.g., NVE, VPLS).

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>