Implement EFB copy filter and gamma in hardware backends

Also makes y_scale a dynamic parameter for EFB copies, as it doesn't
make sense to keep it as part of the uid, otherwise we're generating
redundant shaders.

Source/Core/VideoBackends/Software/SWRenderer.cpp

@@ -87,8 +87,7 @@ std::unique_ptr<AbstractPipeline> SWRenderer::CreatePipeline(const AbstractPipel
 }
 
 // Called on the GPU thread
-void SWRenderer::SwapImpl(AbstractTexture* texture, const EFBRectangle& xfb_region, u64 ticks,
-                          float Gamma)
+void SWRenderer::SwapImpl(AbstractTexture* texture, const EFBRectangle& xfb_region, u64 ticks)
 {
   OSD::DoCallbacks(OSD::CallbackType::OnFrame);