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/galileo_defconfig b/configs/galileo_defconfig
index 7de7749..c0a937f 100644
--- a/configs/galileo_defconfig
+++ b/configs/galileo_defconfig
@@ -1,8 +1,8 @@
 CONFIG_X86=y
-CONFIG_NET=y
 CONFIG_NETDEVICES=y
 CONFIG_VENDOR_INTEL=y
 CONFIG_DEFAULT_DEVICE_TREE="galileo"
 CONFIG_TARGET_GALILEO=y
+CONFIG_CMD_NET=y
 CONFIG_OF_CONTROL=y
 CONFIG_ETH_DESIGNWARE=y