net: dsa: Introduce driver for NXP SJA1105 5-port L2 switch

At this moment the following is supported:
* Link state management through phylib
* Autonomous L2 forwarding managed through iproute2 bridge commands.

IP termination must be done currently through the master netdevice,
since the switch is unmanaged at this point and using
DSA_TAG_PROTO_NONE.

Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: Georg Waibel <georg.waibel@sensor-technik.de>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>