mlxsw: spectrum: Expose KVD size for Spectrum-2

Unlike Spectrum-1, the KVD (Key-value database) of Spectrum-2 is not
partitioned, so only expose the entire KVD size. This enables users to
query the total size of the KVD.

Signed-off-by: Amit Cohen <amitc@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>