[llvm] [AMDGPU][GlobalIsel] Introduce isRegType to check for legal types, instead of checking bit width. (PR #68189)

[Jay Foad via llvm-commits]

jayfoad wrote:

> > There is also some relevant discussion on https://reviews.llvm.org/D148096 which introduced isIllegalRegisterType.
> > Do we really need both isIllegalRegisterType and isRegType?
> 
> I think once we replace all usage of isRegisterType we could do without isIllegalRegisterType.

Could you add a TODO comment to isIllegalRegisterType please?

https://github.com/llvm/llvm-project/pull/68189