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/peach-pi_defconfig b/configs/peach-pi_defconfig
index 865f52c..88f5e97 100644
--- a/configs/peach-pi_defconfig
+++ b/configs/peach-pi_defconfig
@@ -3,6 +3,7 @@
 CONFIG_TARGET_PEACH_PI=y
 CONFIG_DEFAULT_DEVICE_TREE="exynos5800-peach-pi"
 CONFIG_SPL=y
+CONFIG_CMD_NET=y
 CONFIG_CMD_CROS_EC=y
 CONFIG_CROS_EC=y
 CONFIG_CROS_EC_SPI=y