GlobalISel: Implement widenScalar for G_UNMERGE_VALUES

For the scalar case only.

Also move the similar G_MERGE_VALUES handling to a separate function
and cleanup to make them look more similar.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@352979 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed