[PATCH][AArch64] implement aarch64 neon instruction class AdvSIMD (shift)

[Tim Northover]

Hi Hao
> Sorry, wrong patches and cc addresses.
> Send with new patches again.

I don't suppose you've got one before you ran clang-format(?) over the
whole file? It makes working out what's actually changed rather
difficult (and I'm not sure I want some of those things changed).

I usually just run it over a selected region I've been editing.

Cheers.

Tim.