mlxsw: reg: Add Policy-Engine Region Association Register

The PERAR register is used to associate a hw region for region_id's.

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