[][MAC80211][External release build]

[Description]
Add external release build flow

[Release-log]
N/A

Change-Id: I9e7f99d972dec580eff7b50f18f1a0bc90487e4d
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/5687836
diff --git a/autobuild_mac80211_release/get_stagingdir_root.mk b/autobuild_mac80211_release/get_stagingdir_root.mk
new file mode 100644
index 0000000..82aae64
--- /dev/null
+++ b/autobuild_mac80211_release/get_stagingdir_root.mk
@@ -0,0 +1,6 @@
+OPENWRT_BUILD = 1
+
+include Makefile
+
+get-staging-dir-root:
+	@echo "$(STAGING_DIR_ROOT)"