[DEBUGINFO, NVPTX] Set `DW_AT_frame_base` to `DW_OP_call_frame_cfa`.

Summary:
For NVPTX target the value of `DW_AT_frame_base` attribute must be set
to `DW_OP_call_frame_cfa`.

Reviewers: tra, jlebar, echristo

Subscribers: jholewinski, JDevlieghere, llvm-commits

Differential Revision: https://reviews.llvm.org/D45785

llvm-svn: 338036