Cycles: OpenCL tweaks

* Reduce kernel arguments size, helps compile for apple nvidia.
* Fix use of unitialized variable in displace kernel.
* Use build flags in opencl kernel md5 hash.
* Reorganize code for kernel feature #defines a bit.

intern/cycles/kernel/kernel_shader.h

@@ -226,7 +226,7 @@ __device void shader_setup_from_displace(KernelGlobals *kg, ShaderData *sd,
 	Ng = triangle_normal_MT(kg, prim, &shader);
 
 	/* force smooth shading for displacement */
-	sd->shader |= SHADER_SMOOTH_NORMAL;
+	shader |= SHADER_SMOOTH_NORMAL;
 
 	/* watch out: no instance transform currently */