[llvm] Reapply [AMDGPU] prevent shrinking udiv/urem if either operand exceeds signed max (PR #119325)

[Jay Foad via llvm-commits]

jayfoad wrote:

> +Reworked getDivNumBits API to return unsigned and change from AtLeast(SignBits)
> to MaxDivBits hint.

Thanks, but please do this as a separate NFC cleanup patch, to keep it separate from your changes which are definitely not NFC. This should help keep things separate in case any more reverts are required...

https://github.com/llvm/llvm-project/pull/119325