mlxsw: spectrum_buffers: Add Spectrum-2 shared buffer configuration

Customize the tables related to shared buffer configuration to match the
current recommendation for Spectrum-2 systems.

Signed-off-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>