[llvm] [Hexagon] Generate signed mask for vshuff/vdeal (PR #159800)

[Brian Cain via llvm-commits]

https://github.com/androm3da approved this pull request.

It would be a good idea to update the release notes to describe this change.  Can we describe how folks using the upper range of unsigned values might see failures and how to fix it in the release notes too?

https://github.com/llvm/llvm-project/pull/159800