mlxsw: reg: Add Policy-Engine Region eRP Register

The PERERP register configures the region eRPs. It can be used, for
example, to enable lookup in the C-TCAM in addition to the A-TCAM.

To be able to perform a lookup in the C-TCAM we need to "use" the eRP
table. This is done by marking the pointer as valid, but zeroing the eRP
table vector.

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>