Move toString() methods to android::hardware namespace

Bug: 36108426
Test: hidl_test passes

Change-Id: Ie86c0f2654cd75b1c4179f303287e50efa89376a
diff --git a/CompoundType.cpp b/CompoundType.cpp
index 8d9b94b..332bada 100644
--- a/CompoundType.cpp
+++ b/CompoundType.cpp
@@ -504,7 +504,7 @@
 
     out.block([&] {
         // include toString for scalar types
-        out << "using ::android::hardware::details::toString;\n"
+        out << "using ::android::hardware::toString;\n"
             << "std::string os;\n";
         out << "os += \"{\";\n";