[NVPTX] Add more precise PTX/SM target attributes

[NVPTX] Add more precise PTX/SM target attributes

Each SM and PTX version is modeled as a subtarget feature/CPU. Additionally,
PTX 3.1 is added as the default PTX version to be out-of-the-box compatible
with CUDA 5.0.

Available CPUs for this target:

  sm_10 - Select the sm_10 processor.
  sm_11 - Select the sm_11 processor.
  sm_12 - Select the sm_12 processor.
  sm_13 - Select the sm_13 processor.
  sm_20 - Select the sm_20 processor.
  sm_21 - Select the sm_21 processor.
  sm_30 - Select the sm_30 processor.
  sm_35 - Select the sm_35 processor.

Available features for this target:

  ptx30 - Use PTX version 3.0.
  ptx31 - Use PTX version 3.1.
  sm_10 - Target SM 1.0.
  sm_11 - Target SM 1.1.
  sm_12 - Target SM 1.2.
  sm_13 - Target SM 1.3.
  sm_20 - Target SM 2.0.
  sm_21 - Target SM 2.1.
  sm_30 - Target SM 3.0.
  sm_35 - Target SM 3.5.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@167699 91177308-0d34-0410-b5e6-96231b3b80d8