AMDGPU: Add AMDGPU HSA Kernel Descriptor

  - Update docs to match llvm coding style
  - Add missing FP16_OVFL bit for gfx9
  - Fix the size of the kernel descriptor in the docs

Differential Revision: https://reviews.llvm.org/D38902


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@315822 91177308-0d34-0410-b5e6-96231b3b80d8

Author: kzhuravl