R600/SI: Custom select 64-bit ADD

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202194 91177308-0d34-0410-b5e6-96231b3b80d8
R600: Don't unconditionally unroll loops with private memory accesses

This causes the size of the scrypt kernel to explode and eats all the
memory on some systems.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202195 91177308-0d34-0410-b5e6-96231b3b80d8