Embree v2.6.2

• Fixed bug triggered by instantiating motion blur geometry.
• Fixed bug in hit UV coordinates of static subdivision geometry.
• Performance improvements when only changing tessellation levels for
  subdivision geometry per frame.
• Added ray packet intersectors for subdivision geometry, resulting in
  improved performance for coherent rays.
• Reduced virtual address space usage for static geometries.
• Fixed some AVX2 code paths when compiling with GCC or CLANG.
• Bugfix for subdiv patches with non-matching winding order.
• Bugfix in ISA detection of AVX512.