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/igep0030_defconfig b/configs/igep0030_defconfig
index 5e1d43d..cd9753d 100644
--- a/configs/igep0030_defconfig
+++ b/configs/igep0030_defconfig
@@ -3,3 +3,4 @@
 CONFIG_TARGET_OMAP3_IGEP00X0=y
 CONFIG_SPL=y
 CONFIG_SYS_EXTRA_OPTIONS="MACH_TYPE=MACH_TYPE_IGEP0030,BOOT_ONENAND"
+CONFIG_CMD_NET=y