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/mx6qarm2_defconfig b/configs/mx6qarm2_defconfig
index f229702..51ab7e3 100644
--- a/configs/mx6qarm2_defconfig
+++ b/configs/mx6qarm2_defconfig
@@ -1,3 +1,4 @@
 CONFIG_ARM=y
 CONFIG_TARGET_MX6QARM2=y
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/freescale/mx6qarm2/imximage.cfg,MX6Q,DDR_MB=2048"
+CONFIG_CMD_NET=y