nitrogen6x: migrate to using device tree

Migrate to using device tree required for further driver model
integration.

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>
diff --git a/configs/nitrogen6dl_defconfig b/configs/nitrogen6dl_defconfig
index 141289f..d7c6e7c 100644
--- a/configs/nitrogen6dl_defconfig
+++ b/configs/nitrogen6dl_defconfig
@@ -34,6 +34,8 @@
 CONFIG_CMD_EXT4_WRITE=y
 CONFIG_CMD_FAT=y
 CONFIG_CMD_FS_GENERIC=y
+CONFIG_OF_CONTROL=y
+CONFIG_DEFAULT_DEVICE_TREE="imx6dl-nitrogen6x"
 CONFIG_ENV_IS_IN_SPI_FLASH=y
 CONFIG_USB_FUNCTION_FASTBOOT=y
 CONFIG_FASTBOOT_BUF_ADDR=0x12000000
@@ -62,4 +64,3 @@
 CONFIG_VIDEO_IPUV3=y
 CONFIG_VIDEO=y
 # CONFIG_VIDEO_SW_CURSOR is not set
-CONFIG_OF_LIBFDT=y