Add PREUPLOAD.cfg AOSP check

This preupload hook warns agains non-AOSP submits.

Extracted from the PREUPLOAD.cfg in system/sepolicy.

Bug: None
Test: None
Change-Id: Iae6658f92ce3db36c12bfe21f65216fe94d914f4
diff --git a/PREUPLOAD.cfg b/PREUPLOAD.cfg
new file mode 100644
index 0000000..3591c7f
--- /dev/null
+++ b/PREUPLOAD.cfg
@@ -0,0 +1,3 @@
+[Hook Scripts]
+aosp_hook = ${REPO_ROOT}/frameworks/base/tools/aosp/aosp_sha.sh ${PREUPLOAD_COMMIT} "."
+