Extract preparer for namespace

Bug: 193228441
Test: m nothing
Change-Id: If00b0595edd48be8c8d3308b87fb920dfb0340ee
diff --git a/android/namespace.go b/android/namespace.go
index d137636..4f727e1 100644
--- a/android/namespace.go
+++ b/android/namespace.go
@@ -27,7 +27,11 @@
 )
 
 func init() {
-	RegisterModuleType("soong_namespace", NamespaceFactory)
+	registerNamespaceBuildComponents(InitRegistrationContext)
+}
+
+func registerNamespaceBuildComponents(ctx RegistrationContext) {
+	ctx.RegisterModuleType("soong_namespace", NamespaceFactory)
 }
 
 // threadsafe sorted list