[AMDGPU] Enable serializing of argument info.

Summary:
- Support serialization of all arguments in machine function info. This
  enables fabricating MIR tests depending on argument info.

Reviewers: arsenm, rampitec

Subscribers: kzhuravl, jvesely, wdng, nhaehnle, yaxunl, dstuttard, tpr, t-tye, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64096

llvm-svn: 364995