Since commit 230dec61 (net/fec: add imx6q enet support) the FEC driver is no 
longer built by default for i.MX SoCs.

Let the FEC driver be built by default again.
Signed-off-by: NFabio Estevam <fabio.estevam@freescale.com>
Suggested-by: NUwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de
Acked-by: NShawn Guo <shawn.guo@linaro.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>