mlxsw: spectrum: Add another partition to KVD linear

The KVD linear is currently partitioned into two partitions. One for
single entries and another for groups of 32 entries.

Add another partition consisting of groups of 512 entries which will
allow us to more accurately represent the nexthop weights in non-equal
cost multi-path routing.

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>