core/Makefile: Add experimental desktop update image option

.. allowing for experimental update images to be produced based on the
value of `PACK_UPDATE_IMAGE_EXPERIMENTAL`

Bug: 368171802
Test: m pack-update-image # w/ option
Flag: EXEMPT desktop only change
Change-Id: I4151408209a9f73c22234ca6ef5a887c2ce0e286
diff --git a/core/Makefile b/core/Makefile
index 90668a1..96123e2 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -7985,9 +7985,14 @@
 # Desktop pack update image hook.
 ifneq (,$(strip $(PACK_DESKTOP_UPDATE_IMAGE)))
 PACK_UPDATE_IMAGE_TARGET := $(PRODUCT_OUT)/android-desktop_update_image.bin
+PACK_UPDATE_IMAGE_ARGS := --noarchive --update
+
+ifneq (,$(strip $(PACK_UPDATE_IMAGE_EXPERIMENTAL)))
+PACK_UPDATE_IMAGE_ARGS += --experimental
+endif # PACK_UPDATE_IMAGE_EXPERIMENTAL
 
 $(PACK_UPDATE_IMAGE_TARGET): $(IMAGES) $(PACK_IMAGE_SCRIPT)
-	$(PACK_IMAGE_SCRIPT) --out_dir $(PRODUCT_OUT) --noarchive --update
+	$(PACK_IMAGE_SCRIPT) --out_dir $(PRODUCT_OUT) $(PACK_UPDATE_IMAGE_ARGS)
 
 PACKED_UPDATE_IMAGE_ARCHIVE_TARGET := $(PACK_UPDATE_IMAGE_TARGET).gz