Add a repo upload hook for checking the mainline code change.

The common utility modules like libstagefright_foundation is
excluded in the list.

Test: repo upload w/ and wo/ changes in mainline path.
Change-Id: I8794bb675808b85e465408aaf36425da52063ec1
diff --git a/PREUPLOAD.cfg b/PREUPLOAD.cfg
new file mode 100644
index 0000000..e63185d
--- /dev/null
+++ b/PREUPLOAD.cfg
@@ -0,0 +1,2 @@
+[Hook Scripts]
+mainline_hook = tools/mainline_hook.sh ${PREUPLOAD_COMMIT} "."