imagebuilder: store package lists in cache directory

Force opkg to store the downloaded repository indizes into the cache
directory as well, this way the IB can be used in an offline setting
once all required files have been cached.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

SVN-Revision: 46912

target/imagebuilder/files/Makefile

@@ -53,6 +53,7 @@ help: FORCE
 
 # override variables from rules.mk
 PACKAGE_DIR:=$(TOPDIR)/packages
+LISTS_DIR:=$(subst $(space),/,$(patsubst %,..,$(subst /,$(space),$(TARGET_DIR))))$(DL_DIR)
 OPKG:= \
   IPKG_NO_SCRIPT=1 \
   IPKG_TMP="$(TMP_DIR)/ipkgtmp" \
@@ -65,6 +66,7 @@ OPKG:= \
 	--force-overwrite \
 	--force-postinstall \
 	--cache $(DL_DIR) \
+	--lists-dir $(LISTS_DIR) \
 	--offline-root $(TARGET_DIR) \
 	--add-dest root:/ \
 	--add-arch all:100 \