[ARM][MVE] Change VPST to use, not def, VPR

Unlike VPT, VPST just uses the current value of VPR.P0.

Differential Revision: https://reviews.llvm.org/D69037

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@375087 91177308-0d34-0410-b5e6-96231b3b80d8
13 files changed