Add OMNI_PRODUCT_PROPERTIES to product.prop soong

Change-Id: I7919c769e4cf190b466f4d0a4ddbef2cc4211b4a
diff --git a/scripts/gen_build_prop.py b/scripts/gen_build_prop.py
index a793194..d47793a 100644
--- a/scripts/gen_build_prop.py
+++ b/scripts/gen_build_prop.py
@@ -575,6 +575,7 @@
   # TODO(b/117892318): don't allow duplicates so that the ordering doesn't matter
   variables = [
     "ADDITIONAL_PRODUCT_PROPERTIES",
+    "OMNI_PRODUCT_PROPERTIES",
     "PRODUCT_PRODUCT_PROPERTIES",
   ]