mlxsw: reg: add the Monitoring Packet Sampling Configuration Register

The MPSC register allows to configure ingress packet sampling on specific
port of the mlxsw device. The sampled packets are then trapped via
PKT_SAMPLE trap.

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