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/O2MNT_O2M112_defconfig b/configs/O2MNT_O2M112_defconfig
index b17330a..a1ee009 100644
--- a/configs/O2MNT_O2M112_defconfig
+++ b/configs/O2MNT_O2M112_defconfig
@@ -2,3 +2,4 @@
 CONFIG_MPC5xxx=y
 CONFIG_TARGET_O2MNT=y
 CONFIG_SYS_EXTRA_OPTIONS="IFM_SENSOR_TYPE=\"O2M112\""
+CONFIG_CMD_NET=y