build: envsetup: add merge_upstream

Change-Id: I97feb109fc9fe5eb1c6738aaf1477d28681fb9a6
Signed-off-by: Alexander Martinz <amartinz@shiftphones.com>
diff --git a/build/envsetup.sh b/build/envsetup.sh
index 7d115bc..9d75fe4 100644
--- a/build/envsetup.sh
+++ b/build/envsetup.sh
@@ -117,7 +117,14 @@
     generate_changelog HEAD "${1}"
 }
 
-function repopick() {
+function merge_upstream()
+{
+    T=$(gettop)
+    "$T/vendor/shiftos/tools/merge_upstream.py" "$@"
+}
+
+function repopick()
+{
     T=$(gettop)
     "$T/vendor/shiftos/tools/repopick.py" "$@"
 }