arm64: imx: imx8mn-beacon: Migrate to OF_UPSTREAM

The imx8mn-beacon boards can migrate to OF_UPSTREAM which also
allows for the removal the device tree files.

Signed-off-by: Adam Ford <aford173@gmail.com>
diff --git a/configs/imx8mn_beacon_defconfig b/configs/imx8mn_beacon_defconfig
index ec93301..ed671cf 100644
--- a/configs/imx8mn_beacon_defconfig
+++ b/configs/imx8mn_beacon_defconfig
@@ -11,7 +11,7 @@
 CONFIG_ENV_SIZE=0x2000
 CONFIG_ENV_OFFSET=0xFFFFDE00
 CONFIG_DM_GPIO=y
-CONFIG_DEFAULT_DEVICE_TREE="imx8mn-beacon-kit"
+CONFIG_DEFAULT_DEVICE_TREE="freescale/imx8mn-beacon-kit"
 CONFIG_SPL_TEXT_BASE=0x912000
 CONFIG_TARGET_IMX8MN_BEACON=y
 CONFIG_OF_LIBFDT_OVERLAY=y