[Kernel] Make XexUnloadImage fully release the image

Previously XexUnloadImage did not cleanup the image fully,
and if XexLoadImage was to be called again on the same module,
it was not initialized fully, leading to a crash when using it.

src/xenia/kernel/kernel_state.h

@@ -131,6 +131,8 @@ class KernelState {
   void SetExecutableModule(object_ref<UserModule> module);
   object_ref<UserModule> LoadUserModule(const char* name,
                                         bool call_entry = true);
+  void UnloadUserModule(const object_ref<UserModule>& module,
+                        bool call_entry = true);
 
   object_ref<KernelModule> GetKernelModule(const char* name);
   template <typename T>