Core: Hide determinism global

This is only ever queried and not set outside of the Core.cpp, so this
should just be hidden internally and just have a function exposed that
allows querying it.

Source/Core/Core/HW/HW.cpp

@@ -50,7 +50,7 @@ void Init()
 
   if (SConfig::GetInstance().bWii)
   {
-    Core::InitializeWiiRoot(Core::g_want_determinism);
+    Core::InitializeWiiRoot(Core::WantsDeterminism());
     IOS::Init();
     IOS::HLE::Init();  // Depends on Memory
   }