[LV][VPlan] When the load/store stride is -1, use vle/vse instead of vlse/vsse#130032

LiqinWeng wants to merge 2 commits intollvm:mainllvm/llvm-project:mainfrom

LiqinWeng:vprevere-convert-to-unitmemoryLiqinWeng/llvm-project:vprevere-convert-to-unitmemoryCopy head branch name to clipboard