[llvm] [AMDGPU] Handle `s_setreg_imm32_b32` targeting `MODE` register (PR #174681)

[Stanislav Mekhanoshin via llvm-commits]

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

OK, there is one situation where it will miss it, if the SETREG updates MSBs and we do not have a most recent instruction, but I guess this is not a problem because SETREG should not be used this way in a compilation flow anyway, it will break much more things.

Given that SETREG is not going to co-execute with a VALU I guess it also worth nothing that we do not record old MSBs in it.

LGTM.

https://github.com/llvm/llvm-project/pull/174681