[llvm] [ARM] Create DeadRegisterPass for ARM (PR #155530)

[via llvm-commits]

AZero13 wrote:

Basically when we remove a redundant instruction, we end up orphaning the destination sometimes and while one can argue why not have peephole do it there, well it's really because it's easier for me to modify deadregpass to work on ARM by replacing the instruction wholesale than trying to work the logic in the peephole already. 

https://github.com/llvm/llvm-project/pull/155530