LightingShaderGen: Always calculate lighting for both color channels

Cel-damage depends on lighting being calculated for the first channel
even though there is no color in the vertex format (defaults to the
material color). If lighting for the channel is not enabled, the vertex
will use the default color as before.

The default value of the color is determined by the number of elements in
the vertex format. This fixes the grey cubes in Super Mario Sunshine.

If the color channel count is zero, we set the color to black before the
end of the vertex shader. It's possible that this would be undefined
behavior on hardware if a vertex color index that was greater than the
channel count was used within TEV.

Source/Core/VideoCommon/ConstantManager.h

@@ -58,7 +58,7 @@ struct VertexShaderConstants
   u32 components;           // .x
   u32 xfmem_dualTexInfo;    // .y
   u32 xfmem_numColorChans;  // .z
-  u32 pad1;                 // .w
+  u32 color_chan_alpha;     // .w
 
   std::array<float4, 6> posnormalmatrix;
   std::array<float4, 4> projection;