AMDGPU: Use the implicit kernargs for code object version 5

Summary:
  Specifically, for trap handling, for targets that do not support getDoorbellID,
we load the queue_ptr from the implicit kernarg, and move queue_ptr to s[0:1].
To get aperture bases when targets do not have aperture registers, we load
private_base or shared_base directly from the implicit kernarg. In clang, we use
implicitarg_ptr + offsets to implement __builtin_amdgcn_workgroup_size_{xyz}.

Reviewers: arsenm, sameerds, yaxunl

Differential Revision: https://reviews.llvm.org/D120265