Rasterizer: Document SignalFence & ReleaseFences and setup skeletons on Vulkan.

src/video_core/gpu_thread.cpp

@@ -81,9 +81,12 @@ void ThreadManager::SwapBuffers(const Tegra::FramebufferConfig* framebuffer) {
 }
 
 void ThreadManager::FlushRegion(VAddr addr, u64 size) {
+    if (!Settings::IsGPULevelExtreme()) {
+        return;
+    }
     if (system.Renderer().Rasterizer().MustFlushRegion(addr, size)) {
         u64 fence = PushCommand(FlushRegionCommand(addr, size));
-        while (fence < state.signaled_fence.load(std::memory_order_relaxed)) {
+        while (fence > state.signaled_fence.load(std::memory_order_relaxed)) {
         }
     }
 }