[SLP] Don't allow Div/Rem as alternate opcodes

Summary:
We don't have control/verify what will be the RHS of the division, so it might
happen to be zero, causing UB.

Reviewers: Vasilis, RKSimon, ABataev

Reviewed By: ABataev

Subscribers: vporpo, ABataev, hiraditya, llvm-commits, vdmitrie

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D72740