[llvm] [MachineLICM] Hoist copies of constant physical register (PR #93285)

[Luke Lau via llvm-commits]

https://github.com/lukel97 approved this pull request.

Makes sense to me and RISC-V diffs look good. Can't comment on what isConstantPhysReg implies for the other targets though so maybe wait for a 2nd reviewer

https://github.com/llvm/llvm-project/pull/93285