[llvm] [AArch64] Set MaxInterleaving to 4 for Neoverse V2 (PR #100385)

[Sjoerd Meijer via llvm-commits]

sjoerdmeijer wrote:

This now includes lowering the minimum epilogue vectorisation factor from 16 to 8 for the Neoverse V2, which mostly recovers the one regression we spotted in cam4_r. A bit of TTI plumbing and new EpilogueVectorizationMinVF hook is introduced to make this now target specific.

This patch now depends on #108190: it needs the `multiplier` information that is now passed into the profitability calculation:

     bool LoopVectorizationCostModel::isEpilogueVectorizationProfitable(
         const ElementCount VF) const {
         const ElementCount VF, const unsigned Multiplier)

https://github.com/llvm/llvm-project/pull/100385