Restore the diskinstaller dependency, since it's needed for GCE.

Change-Id: Ieb2695afbe551e829357bad56d5fe1501165b495
diff --git a/core/Makefile b/core/Makefile
index de4a268..7116254 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -1242,6 +1242,12 @@
 endif # BOARD_VENDORIMAGE_FILE_SYSTEM_TYPE
 
 # -----------------------------------------------------------------
+# bring in the installer image generation defines if necessary
+ifeq ($(TARGET_USE_DISKINSTALLER),true)
+include bootable/diskinstaller/config.mk
+endif
+
+# -----------------------------------------------------------------
 # host tools needed to build dist and OTA packages
 
 DISTTOOLS :=  $(HOST_OUT_EXECUTABLES)/minigzip \