fixed_pipeline_state: Pack attribute state

Reduce FixedPipelineState's size from 1384 to 664 bytes

src/video_core/engines/maxwell_3d.h

@@ -1149,7 +1149,7 @@ public:
 
                     /// Returns whether the vertex array specified by index is supposed to be
                     /// accessed per instance or not.
-                    bool IsInstancingEnabled(u32 index) const {
+                    bool IsInstancingEnabled(std::size_t index) const {
                         return is_instanced[index];
                     }
                 } instanced_arrays;