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/crownbay_defconfig b/configs/crownbay_defconfig
index 9804ea7..d3a370d 100644
--- a/configs/crownbay_defconfig
+++ b/configs/crownbay_defconfig
@@ -3,4 +3,5 @@
 CONFIG_DEFAULT_DEVICE_TREE="crownbay"
 CONFIG_TARGET_CROWNBAY=y
 CONFIG_GENERATE_PIRQ_TABLE=y
+CONFIG_CMD_NET=y
 CONFIG_OF_CONTROL=y