build: Support packaging for system_root_image.

If system image contains the root directory
(BOARD_BUILD_SYSTEM_ROOT_IMAGE == "true"), we package the root directory
into ROOT/ instead of BOOT/RAMDISK/ in the target_files zip.

Change-Id: I817776ca97194991308b2131d0e34ab136283464
diff --git a/core/Makefile b/core/Makefile
index d43cb78..f7f6e48 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -1435,8 +1435,14 @@
 endif
 	@# Components of the boot image
 	$(hide) mkdir -p $(zip_root)/BOOT
+ifeq ($(BOARD_BUILD_SYSTEM_ROOT_IMAGE),true)
+	$(hide) mkdir -p $(zip_root)/ROOT
+	$(hide) $(call package_files-copy-root, \
+		$(TARGET_ROOT_OUT),$(zip_root)/ROOT)
+else
 	$(hide) $(call package_files-copy-root, \
 		$(TARGET_ROOT_OUT),$(zip_root)/BOOT/RAMDISK)
+endif
 ifdef INSTALLED_KERNEL_TARGET
 	$(hide) $(ACP) $(INSTALLED_KERNEL_TARGET) $(zip_root)/BOOT/kernel
 endif
@@ -1528,7 +1534,11 @@
 	@# and recovery ramdisk files in the zip, and save the output
 	$(hide) zipinfo -1 $@ | awk 'BEGIN { FS="SYSTEM/" } /^SYSTEM\// {print "system/" $$2}' | $(HOST_OUT_EXECUTABLES)/fs_config -C -S $(SELINUX_FC) > $(zip_root)/META/filesystem_config.txt
 	$(hide) zipinfo -1 $@ | awk 'BEGIN { FS="VENDOR/" } /^VENDOR\// {print "vendor/" $$2}' | $(HOST_OUT_EXECUTABLES)/fs_config -C -S $(SELINUX_FC) > $(zip_root)/META/vendor_filesystem_config.txt
+ifeq ($(BOARD_BUILD_SYSTEM_ROOT_IMAGE),true)
+	$(hide) zipinfo -1 $@ | awk 'BEGIN { FS="ROOT/" } /^ROOT\// {print $$2}' | $(HOST_OUT_EXECUTABLES)/fs_config -C -S $(SELINUX_FC) > $(zip_root)/META/root_filesystem_config.txt
+else
 	$(hide) zipinfo -1 $@ | awk 'BEGIN { FS="BOOT/RAMDISK/" } /^BOOT\/RAMDISK\// {print $$2}' | $(HOST_OUT_EXECUTABLES)/fs_config -C -S $(SELINUX_FC) > $(zip_root)/META/boot_filesystem_config.txt
+endif
 	$(hide) zipinfo -1 $@ | awk 'BEGIN { FS="RECOVERY/RAMDISK/" } /^RECOVERY\/RAMDISK\// {print $$2}' | $(HOST_OUT_EXECUTABLES)/fs_config -C -S $(SELINUX_FC) > $(zip_root)/META/recovery_filesystem_config.txt
 	$(hide) (cd $(zip_root) && zip -q ../$(notdir $@) META/*filesystem_config.txt)
 	$(hide) PATH=$(foreach p,$(INTERNAL_USERIMAGES_BINARY_PATHS),$(p):)$$PATH MKBOOTIMG=$(MKBOOTIMG) \