[llvm] [X86] VPTERNLOG comments - use "mem" just for full width loads and "bst32" / "bst64" (PR #143721)

[Phoebe Wang via llvm-commits]

phoebewang wrote:

> m32bcst/m64bcst sgtm - shall we go with that then? (it should work if we want to do this for broadcasts in other instruction comments as well).

I'm fine with broadcasts change. Do we also want to change normal memory to m32/64... We have a few instructions like VCVTPS2PD that memory size not equals to register size, but most of them can be inferred from register size.

https://github.com/llvm/llvm-project/pull/143721