mlxsw: spectrum_acl: Implement basic ERP rehash hits creation

Introduce an initial implementation of rehash logic in ERP code.
Currently, the rehash is considered as needed only in case number of
roots in the hints is smaller than the number of roots actually in use.
In that case return hints pointer and let it be obtained through the
callpath through the Spectrum-2 TCAM op.

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>