add SMSC LAN9x1x Network driver

This patch adds a driver for the following smsc network controllers:
LAN9115
LAN9116
LAN9117
LAN9215
LAN9216
LAN9217

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Guennadi Liakhovetski <lg@denx.de>