mlxsw: spectrum_fid: Add an op to get PGT allocation size

mlxsw: spectrum_fid: Add an op to get PGT allocation size

In the CFF flood mode, the PGT allocation size of RFID family will not
depend on number of FIDs, but rather number of ports and LAGs. Therefore
introduce a FID family operation to calculate the PGT allocation size.

The way that size is calculated in the CFF mode depends on calling fallible
functions. Thus express the op as returning an int, with the size returned
via a pointer argument.

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/1174651b7160fcedbef50010ae4b68201112fe6f.1701183892.git.petrm@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>