Add icache prefetch operations to AArch64

This adds hints to the various "prfm" instructions so that they can
affect the instruction cache as well as the data cache.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174495 91177308-0d34-0410-b5e6-96231b3b80d8
Add AArch64 CRC32 instructions

These instructions are a late addition to the architecture, and may
yet end up behind an optional attribute, but for now they're available
at all times.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174496 91177308-0d34-0410-b5e6-96231b3b80d8