net: Move the CMD_NET config to defconfigs

This also selects CONFIG_NET for any CONFIG_CMD_NET board.

Remove the imx default for CONFIG_NET.

This moves the config that was defined by 60296a8 (commands: add more
command entries in Kconfig).

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/configs/snow_defconfig b/configs/snow_defconfig
index 0ae2b9b..6f838a9 100644
--- a/configs/snow_defconfig
+++ b/configs/snow_defconfig
@@ -3,6 +3,7 @@
 CONFIG_TARGET_SNOW=y
 CONFIG_DEFAULT_DEVICE_TREE="exynos5250-snow"
 CONFIG_SPL=y
+CONFIG_CMD_NET=y
 CONFIG_CMD_SOUND=y
 CONFIG_CMD_CROS_EC=y
 CONFIG_CROS_EC=y