hikey960: Migrate hikey960 build to use Image.gz-dtb kernels

For the UEFI transition we need to move to Image.gz-dtb kernels,
instead of using the separate dts partition as used w/ the HiSi
bootloader.

This patch depends on a Image.gz-dtb-hikey960-4.9/4 kernel to be
in hikey-kernel, but can be used with HiSi bootloader as long
as the dt.img is still flashed.

Change-Id: I8c9ab8a7df516c84c6c5dac57e80388d4d2e40a0
Signed-off-by: John Stultz <john.stultz@linaro.org>
diff --git a/hikey960.mk b/hikey960.mk
index 0612447..1b9799b 100644
--- a/hikey960.mk
+++ b/hikey960.mk
@@ -1,7 +1,7 @@
 ifndef TARGET_KERNEL_USE
 TARGET_KERNEL_USE=4.9
 endif
-TARGET_PREBUILT_KERNEL := device/linaro/hikey-kernel/Image.gz-hikey960-$(TARGET_KERNEL_USE)
+TARGET_PREBUILT_KERNEL := device/linaro/hikey-kernel/Image.gz-dtb-hikey960-$(TARGET_KERNEL_USE)
 TARGET_PREBUILT_DTB := device/linaro/hikey-kernel/hi3660-hikey960.dtb-$(TARGET_KERNEL_USE)
 
 ifeq ($(TARGET_KERNEL_USE), 4.4)