mlxsw: spectrum: Use CFF mode where available

Mark all Spectrum>2 systems as preferring CFF flood mode if supported by
the firmware.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Amit Cohen <amcohen@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://lore.kernel.org/r/8a3d2ad96b943f7e3f53f998bd333a14e19cd641.1701183892.git.petrm@nvidia.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>