mlxsw: spectrum: Add support for new ethtool API

Remove the deprecated {get,set}_settings callbacks and instead add
{get,set}_link_ksettings along with support for newly available speeds.

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>