arm: highbank: Add devicetree files

Add an empty version of this file, so that we can at least build this
board when devicetrees are required.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/highbank_defconfig b/configs/highbank_defconfig
index 85b42c7..af40f71 100644
--- a/configs/highbank_defconfig
+++ b/configs/highbank_defconfig
@@ -7,6 +7,7 @@
 CONFIG_SYS_MALLOC_LEN=0x80000
 CONFIG_NR_DRAM_BANKS=2
 CONFIG_ENV_SIZE=0x2000
+CONFIG_DEFAULT_DEVICE_TREE="highbank"
 CONFIG_SYS_BOOTCOUNT_ADDR=0xfff3cf0c
 CONFIG_SYS_BOOTCOUNT_SINGLEWORD=y
 CONFIG_DISTRO_DEFAULTS=y