[llvm] [LV] Support scalable interleave groups for factors 3, 5, 6 and 7 (PR #141865)

[Luke Lau via llvm-commits]

lukel97 wrote:

> FYI we might start looking into allowing interleaving up to a factor of 8 on AArch64, so what is currently dead code might not be so for very long after this is merged. It's not confirmed though.

Up to 8 will still be covered, do you plan on handling interleave factors > 8? I've added a test to exercise a scalable VF with factor 16 in 203d204b39ad80de14ec5be73ea9be2efd8c4bd2 anyway.

It turns out that even if the TTI hooks allow a higher factor in `getInterleavedMemoryOpCost`, `MaxInterleaveGroupFactor` in VectorUtils.cpp is capped at 8 anyway, so it needs to be overridden from the command line. It doesn't look like there's a TTI hook for this yet

https://github.com/llvm/llvm-project/pull/141865