CS89x0 : add CS89x0 platform device to the iMX31ADS board

Add CS89x0 networking support to the iMX31ADS board by using the
platform driver support in the CS89x0 driver.

Signed-off-by: Jaccon Bastiaansen <jaccon.bastiaansen@gmail.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>