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/pico-pi-imx6ul_defconfig b/configs/pico-pi-imx6ul_defconfig
index 51be1ac..5e18dcc 100644
--- a/configs/pico-pi-imx6ul_defconfig
+++ b/configs/pico-pi-imx6ul_defconfig
@@ -57,6 +57,7 @@
 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