mlxsw: spectrum_router: Move RIFs array to its rightful place

The router interfaces (RIFs) array is of no interest to code outside the
routing realm, so declare it inside the router specific struct instead
of the chip-wide one.

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