AMDGPU/NFC: Minor clean ups in PAL metadata

  - Move PAL metadata definitions to AMDGPUMetadata
  - Make naming consistent with HSA metadata

Differential Revision: https://reviews.llvm.org/D38745


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@315523 91177308-0d34-0410-b5e6-96231b3b80d8
16 files changed