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/somlabs_visionsom_6ull_defconfig b/configs/somlabs_visionsom_6ull_defconfig
index 1a02023..7dad016 100644
--- a/configs/somlabs_visionsom_6ull_defconfig
+++ b/configs/somlabs_visionsom_6ull_defconfig
@@ -42,6 +42,7 @@
 CONFIG_PHYLIB=y
 CONFIG_PHY_MICREL=y
 CONFIG_PHY_MICREL_KSZ8XXX=y
+CONFIG_FEC_MXC=y
 CONFIG_MII=y
 CONFIG_PINCTRL=y
 CONFIG_PINCTRL_IMX6=y