net: dsa: sja1105: Add support for FDB and MDB management

Currently only the (more difficult) first generation E/T series is
supported. Here the TCAM is only 4-way associative, and to know where
the hardware will search for a FDB entry, we need to perform the same
hash algorithm in order to install the entry in the correct bin.

On P/Q/R/S, the TCAM should be fully associative. However the SPI
command interface is different, and because I don't have access to a
new-generation device at the moment, support for it is TODO.

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