[clang][AMDGPU]: Don't use byval for struct arguments in function ABI

Summary:
  Byval requires allocating additional stack space, and always requires an implicit copy to be inserted in codegen,
where it can be difficult to optimize. In this work, we use byref/IndirectAliased promotion method instead of
byval with the implicit copy semantics.

Reviewers:
  arsenm

Differential Revision:
  https://reviews.llvm.org/D155986