[llvm] [AMDGPU][GlobalISel] Allow forming s16 U/SBFX pre-regbankselect (PR #131309)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

We don't have 16-bit BFE instructions, so I don't understand why you would do this 

https://github.com/llvm/llvm-project/pull/131309