[AArch64][LoopVectorize] Enable tail-folding of simple loops on neoverse-v1

[AArch64][LoopVectorize] Enable tail-folding of simple loops on neoverse-v1

This patch enables the tail-folding of simple loops by default
when targeting the neoverse-v1 CPU. Simple loops exclude those
with recurrences or reductions or loops that are reversed.

New tests have been added here:

Transforms/LoopVectorize/AArch64/sve-tail-folding-option.ll

In terms of SPEC2017 only one benchmark is really affected when
building with "-Ofast -mcpu=neoverse-v1 -flto", which is
(+ faster, - slower):

525.x264: +7.0%

Differential Revision: https://reviews.llvm.org/D130618