[DEBUG_INFO][NVPTX]Fix processing of DBG_VALUES.

Summary:
If the instruction in the eliminateFrameIndex function is a DBG_VALUE
instruction, it requires special processing. The frame register is set
to VRFrame and the offset is based on the object offset.
The code is similar to the code used in
lib/CodeGen/PrologEpilogInserter.cpp.

Reviewers: tra

Subscribers: jholewinski, llvm-commits

Differential Revision: https://reviews.llvm.org/D53657

llvm-svn: 345269