mlxsw: spectrum_acl: Enable C-TCAM only mode in eRP core

Currently, no calls are performed into the eRP core, but in order to
make review easier we would like to gradually add these calls.

Have the eRP core initialize a region's master mask to all ones and
allow it to use an empty eRP table. This directs the lookup to the
C-TCAM and allows the C-TCAM only mode to continue working.

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