mlxsw: reg: Add The Router TCAM Allocation register

This register is used for allocation of regions in the TCAM table and it
will be used by the multicast router offloading logic.

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>