mlxsw: reg: Extract flood-mode specific part of mlxsw_reg_sfmr_pack()

In CFF mode, it is necessary to set a different set of SFMR fields. Leave
in mlxsw_reg_sfmr_pack() only the common bits, and move the parts relevant
to controlled flood mode directly to the call site.

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/6f29639ebc3ca0722272e6c644ca910096469413.1700503644.git.petrm@nvidia.com


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