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/chromebook_link_defconfig b/configs/chromebook_link_defconfig
index 3d2bdf6..4f7f779 100644
--- a/configs/chromebook_link_defconfig
+++ b/configs/chromebook_link_defconfig
@@ -5,6 +5,7 @@
 CONFIG_HAVE_MRC=y
 CONFIG_FRAMEBUFFER_SET_VESA_MODE=y
 CONFIG_FRAMEBUFFER_VESA_MODE_11A=y
+CONFIG_CMD_NET=y
 CONFIG_OF_CONTROL=y
 CONFIG_DM_PCI=y
 CONFIG_VIDEO_VESA=y