mlxsw: reg: Add Policy-Engine Policy Based Switching Register

The PPBS register retrieves and sets Policy Based Switching Table entries.

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