include: update xgl.h with FF vertex fetch
include: update xgl.h with FF vertex fetch

https://cvs.khronos.org/svn/repos/oglc/trunk/nextgen/proposals/IMG/xgl_vertex_input_description2_img.h

KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools