image: fix CONFIG_CLEAN_IPKG with CONFIG_TARGET_PER_DEVICE_ROOTFS

Running prepare_rootfs on TARGET_DIR deletes the opkg state when
CONFIG_CLEAN_IPKG is enabled, making the per-device rootfs package install
fail.

To avoid this, create a copy of the TARGET_DIR before prepare_rootfs is run
and use this as basis for per-device rootfs generation.

Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>

include/image.mk

@@ -297,7 +297,7 @@ opkg_target = \
 
 target-dir-%: FORCE
 	rm -rf $(mkfs_cur_target_dir) $(mkfs_cur_target_dir).opkg
-	$(CP) $(TARGET_DIR) $(mkfs_cur_target_dir)
+	$(CP) $(TARGET_DIR_ORIG) $(mkfs_cur_target_dir)
 	-mv $(mkfs_cur_target_dir)/etc/opkg $(mkfs_cur_target_dir).opkg
 	echo 'src default file://$(PACKAGE_DIR_ALL)' > $(mkfs_cur_target_dir).conf
 	$(if $(call opkg_package_files,$(mkfs_packages_add)), \

include/rootfs.mk

@@ -52,6 +52,8 @@ opkg_package_files = $(wildcard \
 	$(foreach dir,$(PACKAGE_SUBDIRS), \
 	  $(foreach pkg,$(1), $(dir)/$(pkg)_*.ipk)))
 
+TARGET_DIR_ORIG := $(TARGET_ROOTFS_DIR)/root.orig-$(BOARD)
+
 define prepare_rootfs
 	@if [ -d $(TOPDIR)/files ]; then \
 		$(call file_copy,$(TOPDIR)/files/.,$(1)); \