Add make sync target

make sync will build everything necessary to adb sync system
and vendor, without wasting time rebuilding system.img and
vendor.img.

Test: m -j sync
Change-Id: I91c0012eed6d58a338393cc375056a30e2a24b09
diff --git a/core/Makefile b/core/Makefile
index a23cdd4..b0d1b34 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -1235,7 +1235,6 @@
     $(PDK_FUSION_SYSIMG_FILES) \
     $(RECOVERY_RESOURCE_ZIP))
 
-
 FULL_SYSTEMIMAGE_DEPS := $(INTERNAL_SYSTEMIMAGE_FILES) $(INTERNAL_USERIMAGES_DEPS)
 
 # ASAN libraries in the system image - add dependency.
@@ -1357,6 +1356,9 @@
 endif
 endif
 
+.PHONY: sync
+sync: $(INTERNAL_SYSTEMIMAGE_FILES)
+
 #######
 ## system tarball
 define build-systemtarball-target
@@ -1739,6 +1741,8 @@
 vendorimage-nodeps vnod: | $(INTERNAL_USERIMAGES_DEPS) $(DEPMOD)
 	$(build-vendorimage-target)
 
+sync: $(INTERNAL_VENDORIMAGE_FILES)
+
 else ifdef BOARD_PREBUILT_VENDORIMAGE
 INSTALLED_VENDORIMAGE_TARGET := $(PRODUCT_OUT)/vendor.img
 $(eval $(call copy-one-file,$(BOARD_PREBUILT_VENDORIMAGE),$(INSTALLED_VENDORIMAGE_TARGET)))