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/liteboard_defconfig b/configs/liteboard_defconfig
index 0381e64..ab62c20 100644
--- a/configs/liteboard_defconfig
+++ b/configs/liteboard_defconfig
@@ -50,6 +50,7 @@
 CONFIG_PHYLIB=y
 CONFIG_PHY_SMSC=y
 CONFIG_DM_ETH=y
+CONFIG_FEC_MXC=y
 CONFIG_MII=y
 CONFIG_PINCTRL=y
 CONFIG_PINCTRL_IMX6=y