iris: setup EdgeFlag Vertex Element when needed.

If Vertex Shader uses EdgeFlag the hardware request that it is setup as the last VERTEX_ELEMENT_STATE. If SGVS are add at draw time we need to also reconfigure the last 3DSTATE_VF_INSTANCING so its VertexElementIndex points to the new Vertex Element that contains the EdgeFlag.

So if draw parameters or edgeflag are not used the CSO generated at iris_create_vertex_element is sent directly in the batches. But if edge flag is used we adjust last VERTEX_ELEMENT_STATE and last 3DSTATE_VF_INSTANCING using their alternative edge flag version we generate at iris_create_vertex_element and store at the CSO.