kernel: Allow overriding dtbo target name

gs101 kernel uses google/dtbo.img target for dtbo.img

Change-Id: Ib03f35c0035f56d303771de9399bcce3d02c0775

build/tasks/kernel.mk

@@ -428,7 +428,7 @@ else
 	$(MKDTBOIMG) create $@ --page_size=$(BOARD_KERNEL_PAGESIZE) $(shell find $(DTBO_OUT)/arch/$(KERNEL_ARCH)/boot/dts -type f -name "*.dtbo" | sort)
 endif # BOARD_DTBO_CFG
 else
-	$(call make-dtbo-target,dtbo.img)
+	$(call make-dtbo-target,$(TARGET_KERNEL_DTBO))
 endif # BOARD_KERNEL_SEPARATED_DTBO
 	$(hide) touch -c $(DTBO_OUT)
 endif # BOARD_CUSTOM_DTBOIMG_MK

config/BoardConfigKernel.mk

@@ -35,6 +35,9 @@
 #                                        makefile. Can be overriden in device trees
 #                                        in the event of prebuilt kernel.
 #
+#   TARGET_KERNEL_DTBO                 = Name of the kernel Makefile target that
+#                                        generates dtbo.img. Defaults to dtbo.img
+#
 #   KERNEL_TOOLCHAIN_PREFIX            = Overrides TARGET_KERNEL_CROSS_COMPILE_PREFIX,
 #                                          Set this var in shell to override
 #                                          toolchain specified in BoardConfig.mk
@@ -148,7 +151,8 @@ endif
 
 # Set DTBO image locations so the build system knows to build them
 ifeq (true,$(filter true, $(TARGET_NEEDS_DTBOIMAGE) $(BOARD_KERNEL_SEPARATED_DTBO)))
-BOARD_PREBUILT_DTBOIMAGE ?= $(TARGET_OUT_INTERMEDIATES)/DTBO_OBJ/arch/$(KERNEL_ARCH)/boot/dtbo.img
+TARGET_KERNEL_DTBO ?= dtbo.img
+BOARD_PREBUILT_DTBOIMAGE ?= $(TARGET_OUT_INTERMEDIATES)/DTBO_OBJ/arch/$(KERNEL_ARCH)/boot/$(TARGET_KERNEL_DTBO)
 endif
 
 # Set use the full path to the make command