Fix llvm.aarch64.irg properties.

Summary:
IRG does not access any memory.
Replace IntrInaccessibleMemOnly with IntrNoMem | IntrHasSideEffects.

Reviewers: chill

Subscribers: javed.absar, kristof.beyls, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64447

llvm-svn: 368362