mlxsw: spectrum: Add the multicast routing hardware logic

Implement the multicast routing hardware API introduced in previous patch
for the specific spectrum hardware.

The spectrum hardware multicast routes are written using the RMFT2 register
and point to an ACL flexible action set. The actions used for multicast
routes are:
 - Counter action, which allows counting bytes and packets on multicast
   routes.
 - Multicast route action, which provide RPF check and do the actual packet
   duplication to a list of RIFs.
 - Trap action, in the case the route action specified by the called is
   trap.

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