Allow for the DTB image to be built by the Android build system.

The current solution expects BOARD_PREBUILT_DTBIMAGE_DIR to
contain prebuilt DTB files that are concatenated by the build system
to create $OUT/dtb.img. In order to accommodate devices that build
the dtb image locally, make boot.img creation depend on $OUT/dtb.img
only when BOARD_PREBUILT_DTBIMAGE_DIR is undefined.

Bug: 133161451
Test: Build with BOARD_PREBUILT_DTBIMAGE_DIR undefined and verify
using unpack_bootimg.py that $OUT/dtb.img was included in boot.img.

Change-Id: Iae2c634ccdc1d83589b26d382882f75fb8565a31
diff --git a/core/Makefile b/core/Makefile
index 603ad10..c0a8acc 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -857,12 +857,13 @@
 
 #------------------------------------------------------------------
 # dtb
-
-ifdef BOARD_PREBUILT_DTBIMAGE_DIR
+ifdef BOARD_INCLUDE_DTB_IN_BOOTIMG
 INSTALLED_DTBIMAGE_TARGET := $(PRODUCT_OUT)/dtb.img
+ifdef BOARD_PREBUILT_DTBIMAGE_DIR
 $(INSTALLED_DTBIMAGE_TARGET) : $(sort $(wildcard $(BOARD_PREBUILT_DTBIMAGE_DIR)/*.dtb))
 	cat $^ > $@
 endif
+endif
 
 # -----------------------------------------------------------------
 # the ramdisk
@@ -3820,6 +3821,7 @@
 	    $(INTERNAL_SYSTEMOTHERIMAGE_FILES) \
 	    $(INSTALLED_ANDROID_INFO_TXT_TARGET) \
 	    $(INSTALLED_KERNEL_TARGET) \
+	    $(INSTALLED_DTBIMAGE_TARGET) \
 	    $(INSTALLED_2NDBOOTLOADER_TARGET) \
 	    $(BOARD_PREBUILT_DTBOIMAGE) \
 	    $(BOARD_PREBUILT_RECOVERY_DTBOIMAGE) \
@@ -3872,7 +3874,7 @@
 ifdef BOARD_INCLUDE_RECOVERY_ACPIO
 	$(hide) cp $(BOARD_RECOVERY_ACPIO) $(zip_root)/$(PRIVATE_RECOVERY_OUT)/recovery_acpio
 endif
-ifdef BOARD_INCLUDE_DTB_IN_BOOTIMG
+ifdef INSTALLED_DTBIMAGE_TARGET
 	$(hide) cp $(INSTALLED_DTBIMAGE_TARGET) $(zip_root)/$(PRIVATE_RECOVERY_OUT)/dtb
 endif
 ifdef INTERNAL_KERNEL_CMDLINE