Snowball: Build device tree file

The tracking build uses the linux-linaro-tracking kernel and needs
a device tree file to boot.

Change-Id: Ia528ea64bbcc0686d4959dcc01a9bfbe6c773e2e
Signed-off-by: Patrik Ryd <patrik.ryd@linaro.org>
diff --git a/BoardConfig.mk b/BoardConfig.mk
index 9852b4b..cb73ee3 100644
--- a/BoardConfig.mk
+++ b/BoardConfig.mk
@@ -7,6 +7,7 @@
 TARGET_NO_BOOTLOADER := true # Uses u-boot instead 
 TARGET_NO_KERNEL := false
 KERNEL_CONFIG := u8500_android_defconfig
+DEVICE_TREES := snowball:board.dtb
 TARGET_USE_UBOOT := true
 UBOOT_CONFIG := snowball_config
 TARGET_USE_XLOADER := false