net/fec: consolidate all i.MX options to CONFIG_ARM

Moreover stop listing all i.MX platforms featuring a FEC, and use
the platform's config symbol that selects registration of a fec device
instead.  This might make it easier to add new platforms.

Set default = y for ARMs having a fec to reduce defconfig sizes.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index 0382332..65027a7 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -1944,7 +1944,8 @@
 config FEC
 	bool "FEC ethernet controller (of ColdFire and some i.MX CPUs)"
 	depends on M523x || M527x || M5272 || M528x || M520x || M532x || \
-		MACH_MX27 || ARCH_MX35 || ARCH_MX25 || ARCH_MX5 || SOC_IMX28
+		IMX_HAVE_PLATFORM_FEC || MXS_HAVE_PLATFORM_FEC
+	default IMX_HAVE_PLATFORM_FEC || MXS_HAVE_PLATFORM_FEC if ARM
 	select PHYLIB
 	help
 	  Say Y here if you want to use the built-in 10/100 Fast ethernet