[llvm] [AArch64] Add costs for ST3 and ST4 instructions, modelled as store(shuffle). (PR #87934)

[David Green via llvm-commits]

davemgreen wrote:

> LGTM - my only remaining thought is whether we need the Args argument now we have CxtI?

I guess that you could know the Args that the shuffle will use without knowing/having the exact shuffle instruction already, so it might still be useful to keep.

https://github.com/llvm/llvm-project/pull/87934