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/Null/Render.cpp

@@ -92,7 +92,7 @@ TargetRectangle Renderer::ConvertEFBRectangle(const EFBRectangle& rc)
   return result;
 }
 
-void Renderer::SwapImpl(AbstractTexture*, const EFBRectangle&, u64, float)
+void Renderer::SwapImpl(AbstractTexture*, const EFBRectangle&, u64)
 {
   UpdateActiveConfig();
 }