[llvm] [AMDGPU][Legalizer] Widen i16 G_SEXT_INREG (PR #131308)

[Jay Foad via llvm-commits]

https://github.com/jayfoad commented:

Looks reasonable. Should we do this for _any_ type smaller than i32, instead of just i16 specifically?

https://github.com/llvm/llvm-project/pull/131308