[AArch64][LoopVectorize] Introduce trip count minimal value threshold to ignore tail-folding.

After D121595 was commited, I noticed regressions assosicated with small trip
count numbersvectorisation by tail folding with scalable vectors. As a solution
for those issues I propose to introduce the minimal trip count threshold value.

  Differential Revision: https://reviews.llvm.org/D130755

(cherry picked from commit cab6cd68)