Convert CONFIG_FEC_MXC to Kconfig

This converts the following to Kconfig:
	CONFIG_FEC_MXC

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/m53menlo_defconfig b/configs/m53menlo_defconfig
index 4492b91..193c63e 100644
--- a/configs/m53menlo_defconfig
+++ b/configs/m53menlo_defconfig
@@ -90,6 +90,7 @@
 CONFIG_DM_ETH=y
 CONFIG_DM_MDIO=y
 CONFIG_DM_ETH_PHY=y
+CONFIG_FEC_MXC=y
 CONFIG_PINCTRL=y
 CONFIG_PINCTRL_IMX5=y
 CONFIG_DM_REGULATOR=y