mlxsw: spectrum_fid: Add an op to get PGT address of a FID

In the CFF flood mode, the way to determine a PGT address where a given FID
/ flood table resides is different from the controlled flood mode, which
mlxsw currently uses. Furthermore, this will differ between rFID family and
bridge families. The operation therefore needs to be dynamically
dispatched. To that end, add an op to FID-family ops.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Amit Cohen <amcohen@nvidia.com>
Link: https://lore.kernel.org/r/00e8f6ad79009a9a77a5c95d596ea9574776dc95.1701183892.git.petrm@nvidia.com


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