net: dsa: sja1105: Add FDB operations for P/Q/R/S series

This adds support for manipulating the L2 forwarding database (dump,
add, delete) for the second generation of NXP SJA1105 switches.

At the moment only FDB entries installed statically through 'bridge fdb'
are visible in the dump callback - the dynamically learned ones are
still under investigation.

Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>