mlxsw: reg: Add Tunneling NVE General Configuration Register

This register configures global NVE configuration such as source IP of
the NVE tunnel and UDP source port calculation.

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