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_globals.h

@@ -77,8 +77,7 @@ typedef struct KernelGlobals {
 	__constant KernelData *data;
 
 #define KERNEL_TEX(type, ttype, name) \
-	__global type *name; \
-	int name##_width;
+	__global type *name;
 #include "kernel_textures.h"
 } KernelGlobals;