mlxsw: spectrum_fid: Configure flooding entries using PGT APIs

The PGT (Port Group Table) table maps an index to a bitmap of local ports
to which a packet needs to be replicated. This table is used for layer 2
multicast and flooding.

In the legacy model, software did not interact with PGT table directly.
Instead, it was accessed by firmware in response to registers such as SFTR
and SMID. In the new model, the SFTR register is deprecated and software
has full control over the PGT table using the SMID register.

Use the new PGT APIs to allocate entries for flooding as part of flood
tables initialization. Add mlxsw_sp_fid_flood_tables_fini() to free the
allocated indexes. In addition, use PGT APIs to add/remove ports from PGT
table. The existing code which configures the flood entries via SFTR2 will
be removed later.

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: Paolo Abeni <pabeni@redhat.com>