mlxsw: reg: Add 'flood_rsp' field to SFMR register

SFMR register creates and configures FIDs. As preparation for unified
bridge model, add a field for future use.

In the new model, RITR no longer configures the rFID used for sub-port RIFs
and it has to be created by software via SFMR. Such FIDs need to be created
with special flood indication using 'flood_rsp' field. When set, this bit
instructs the device to manage the flooding entries for this FID in a
reserved part of the port group table (PGT).

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>