mlxsw: Enable unified bridge model

After all the preparations for unified bridge model, finally flip mlxsw
driver to use the new model.

Change config profile, set 'ubridge' to true and remove the configurations
that are relevant only for the legacy model. Set 'flood_mode' to
'controlled' as the current mode is not supported with unified bridge
model.

Remove all the code which is dedicated to the legacy model. Remove
'struct mlxsw_sp.ubridge' variable which was temporarily added to separate
configurations between the models.

Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>