Add operator== and != for some structs.

operator== and != are defined for type T where T is
one of the following:
* scalars
* strings
* enums
* U[] where U is in this list
* vec<U> where U is in this list
* structs that contain only types in this list.

If a struct contains a handle, an MQDescriptor,
or a union, for example, then == and != is not generated.

Bug: 32834072

Test: hidl_test
Change-Id: Icac73a14f81274ee6592e2b8fadf26d629151d9f
diff --git a/Type.cpp b/Type.cpp
index 107e502..54135e0 100644
--- a/Type.cpp
+++ b/Type.cpp
@@ -120,6 +120,10 @@
     return false;
 }
 
+bool Type::canCheckEquality() const {
+    return false;
+}
+
 std::string Type::getCppType(StorageMode, bool) const {
     CHECK(!"Should not be here");
     return std::string();