Cycles Refactor: Add SSE Utility code from Embree for cleaner SSE code.

This makes the code a bit easier to understand, and might come in handy
if we want to reuse more Embree code.

Differential Revision: https://developer.blender.org/D482

Code by Brecht, with fixes by Lockal, Sergey and myself.

intern/cycles/kernel/kernel_avx.cpp

@@ -24,6 +24,7 @@
 #define __KERNEL_SSE3__
 #define __KERNEL_SSSE3__
 #define __KERNEL_SSE41__
+#define __KERNEL_AVX__
 #endif
  
 #include "util_optimization.h"