mlxsw: spectrum: Prevent auto negotiation on number of lanes

After 50G-1-lane and 100G-2-lanes link modes were introduced, the driver
is facing situations in which the hardware auto negotiates not only on
speed and type, but also on number of lanes.

Prevent auto negotiation on number of lanes by allowing only port speeds
that can be supported on a given port according to its width.

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