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/arcangel4_defconfig b/configs/arcangel4_defconfig
index 12dc3f2..f1bfba0 100644
--- a/configs/arcangel4_defconfig
+++ b/configs/arcangel4_defconfig
@@ -4,6 +4,7 @@
 CONFIG_DM_SERIAL=y
 CONFIG_SYS_TEXT_BASE=0x81000000
 CONFIG_DEFAULT_DEVICE_TREE="arcangel4"
+CONFIG_CMD_NET=y
 CONFIG_OF_CONTROL=y
 CONFIG_OF_EMBED=y
 CONFIG_DM=y