mlxsw: reg: Add QoS Priority Trust State Register

The QPTS register controls the port policy to calculate the switch
priority and packet color based on incoming packet fields.

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