Cycles: change svm node decoding for more efficient code generation on GPU

These functions no longer accept NULL. They were renamed for clarity and to
avoid hidden merge issues.

Ref D5363

intern/cycles/kernel/svm/svm_wireframe.h

@@ -93,7 +93,7 @@ ccl_device void svm_node_wireframe(KernelGlobals *kg, ShaderData *sd, float *sta
   uint in_size = node.y;
   uint out_fac = node.z;
   uint use_pixel_size, bump_offset;
-  decode_node_uchar4(node.w, &use_pixel_size, &bump_offset, NULL, NULL);
+  svm_unpack_node_uchar2(node.w, &use_pixel_size, &bump_offset);
 
   /* Input Data */
   float size = stack_load_float(stack, in_size);