mlxsw: reg: Add SPAN encapsulation to MPAT register

MPAT Register is used to query and configure the Switch Port Analyzer
Table. To configure Port Analyzer to encapsulate mirrored packets,
additional fields need to be specified for the MPAT register.

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