[llvm] CodeGen: Pass SubtargetInfo to TargetGenInstrInfo constructors (PR #157337)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Looks good as such, but can you provide more information? What kind of decisions and what new arguments?

getHwMode 

> Should the title mention TargetSubtargetInfo instead of MCSubtargetInfo?

Yes
> 
> Should it be propagated down to the base `TargetInstrInfo`? There are a lot of TII methods that need STI, but currently have to obtain it via MF / MI / MBB.

Thinking about doing that next but it's a separable step

https://github.com/llvm/llvm-project/pull/157337