[NVPTX] Add more surface/texture intrinsics, including CUDA unified texture fetch

This also uses TSFlags to mark machine instructions that are surface/texture
accesses, as well as the vector width for surface operations.  This is used
to simplify some of the switch statements that need to detect surface/texture
instructions

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213256 91177308-0d34-0410-b5e6-96231b3b80d8