Restrict vendor modules to help AOSP product distribution.

Bug: 5692177

If you set "PRODUCT_RESTRICT_VENDOR_FILES := true" in a product
configuration, this changes restricts that:
- No overlays in the vendor tree.
- No PRODUCT_COPY_FILES coming from the vendor tree.
- Any referenced package with Android.mk in the vendor tree must have
  LOCAL_MODULE_OWNER set to a value that's compared against a whitelist
  stored in the core build system.

Change-Id: I172b84c7c853e9a04bf9879ea8dec90bd5054230
diff --git a/core/product.mk b/core/product.mk
index f7c772f..561003d 100644
--- a/core/product.mk
+++ b/core/product.mk
@@ -84,6 +84,7 @@
     PRODUCT_SDK_ADDON_DOC_MODULES \
     PRODUCT_DEFAULT_WIFI_CHANNELS \
     PRODUCT_DEFAULT_DEV_CERTIFICATE \
+    PRODUCT_RESTRICT_VENDOR_FILES \
 
 
 define dump-product