Add a dirty flag for arraybases.

Only loop through and call getPointers when something has actually
changed.
Worth about 2-4% speedup un SMG over the previous commit.

Source/Core/VideoCommon/CPMemory.h

@@ -255,6 +255,7 @@ struct CPState final
 
 	// Attributes that actually belong to VertexLoaderManager:
 	BitSet32 attr_dirty;
+	bool bases_dirty;
 	VertexLoaderBase* vertex_loaders[8];
 };