Add debanding option to improve gradient smoothness with truecolor

This option only has an effect if true color is also enabled.

src/core/gpu_hw_shadergen.h

@@ -11,7 +11,7 @@ public:
   GPU_HW_ShaderGen(RenderAPI render_api, u32 resolution_scale, u32 multisamples, bool per_sample_shading,
                    bool true_color, bool scaled_dithering, GPUTextureFilter texture_filtering, bool uv_limits,
                    bool pgxp_depth, bool disable_color_perspective, bool supports_dual_source_blend,
-                   bool supports_framebuffer_fetch);
+                   bool supports_framebuffer_fetch, bool debanding);
   ~GPU_HW_ShaderGen();
 
   std::string GenerateBatchVertexShader(bool textured);
@@ -51,4 +51,5 @@ private:
   bool m_uv_limits;
   bool m_pgxp_depth;
   bool m_disable_color_perspective;
+  bool m_debanding;
 };