net/fec: make FEC driver buildable as module

Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de>
Tested-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/Kconfig

@@ -21,7 +21,7 @@ config NET_VENDOR_FREESCALE
 if NET_VENDOR_FREESCALE
 
 config FEC
-	bool "FEC ethernet controller (of ColdFire and some i.MX CPUs)"
+	tristate "FEC ethernet controller (of ColdFire and some i.MX CPUs)"
 	depends on (M523x || M527x || M5272 || M528x || M520x || M532x || \
 		   ARCH_MXC || ARCH_MXS)
 	default ARCH_MXC || ARCH_MXS if ARM