net: dsa: felix: program host FDB entries towards PGID_CPU for tag_8021q too

I remembered why we had the host FDB migration procedure in place.

It is true that host FDB entry migration can be done by changing the
value of PGID_CPU, but the problem is that only host FDB entries learned
while operating in NPI mode go to PGID_CPU. When the CPU port operates
in tag_8021q mode, the FDB entries are learned towards the unicast PGID
equal to the physical port number of this CPU port, bypassing the
PGID_CPU indirection.

So host FDB entries learned in tag_8021q mode are not migrated any
longer towards the NPI port.

Fix this by extracting the NPI port -> PGID_CPU redirection from the
ocelot switch lib, moving it to the Felix DSA driver, and applying it
for any CPU port regardless of its kind (NPI or tag_8021q).

Fixes: a51c1c3f ("net: dsa: felix: stop migrating FDBs back and forth on tag proto change")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>