mlxsw: spectrum_acl: Move block items encoding into Spectrum op

Since Spectrum-2 encodes blocks into different HW layout, push this
code into Spectrum-specific op.

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