[SelectionDAG] Transfer DbgValues when integer operations are promoted

Summary:
DbgValue nodes were not transferred when integer DAG nodes were promoted. For example, if an i32 add node was promoted to an i64 add node by DAGTypeLegalizer::PromoteIntegerResult(), its DbgValue node was not transferred to the new node. The simple fix is to update SetPromotedInteger() to transfer DbgValues. 

Add AArch64/dbg-value-i8.ll to test this change and fix ARM/debug-info-d16-reg.ll which had the wrong DILocalVariable nodes with arg numbers even though they are not for function parameters.

Patch by Se Jong Oh!

Reviewers: vsk, JDevlieghere, aprantl

Reviewed By: JDevlieghere

Subscribers: javed.absar, kristof.beyls, llvm-commits

Tags: #debug-info

Differential Revision: https://reviews.llvm.org/D44546

llvm-svn: 327919