[AArch64] Fix stp-opt-with-renaming-ld3.mir with expensive checks.

Unconditionally use -verify-machineinstrs and XFAIL the test until
fixed.

Author: fhahn

llvm/test/CodeGen/AArch64/stp-opt-with-renaming-ld3.mir

@@ -1,4 +1,5 @@
-# RUN: llc -run-pass=aarch64-ldst-opt -mtriple=arm64-apple-iphoneos -aarch64-load-store-renaming=true -o - %s | FileCheck %s
+# XFAIL: *
+# RUN: llc -run-pass=aarch64-ldst-opt -mtriple=arm64-apple-iphoneos -aarch64-load-store-renaming=true -verify-machineinstrs -o - %s | FileCheck %s
 --- |
   define void @test_ld3(<8 x i8>* %a1) {
   entry: