AMDHSA: Code object v3 updates

- Do not emit following assembler directives:
  - .hsa_code_object_version
  - .hsa_code_object_isa
  - .amd_amdgpu_isa
  - .amd_amdgpu_hsa_metadata
  - .amd_amdgpu_pal_metadata
- Do not emit .note entries
- Cleanup and bring in sync kernel descriptor header file
- Emit kernel descriptor into .rodata with appropriate relocations and
  alignments

llvm-svn: 334519