Merge pull request #10977 from tellowkrinkle/FixBackendMultithreading

VideoBackends:Vulkan: Improve backend multithreading

Source/Core/VideoBackends/Vulkan/CommandBufferManager.h

@@ -117,6 +117,7 @@ private:
     u64 fence_counter = 0;
     bool init_command_buffer_used = false;
     bool semaphore_used = false;
+    std::atomic<bool> waiting_for_submit{false};
     u32 frame_index = 0;
 
     std::vector<std::function<void()>> cleanup_resources;