[llvm] [AMDGPU] Give some of the VI V_PK_* instructions a subtarget predicate. (PR #70334)

[Ivan Kosarev via llvm-commits]

kosarev wrote:

> lgtm assuming "part of" implies there's a second patch which adds tests

'Part of' is supposed to mean there will be more patches, but I don't know how to test this now, because reproducing the problem would require changing the order in which instructions are matched in AsmParser. Improving existing ambiguity checks could help with this and is also seen part of the ticket, but doing that first, despite being generally preferable, would significantly delay starting working on the support for structured initialiser syntax, which is now a work of a priority. The plan is therefore that we try to mitigate the immediate problem with added/changed operand classes causing failures on regression tests, then deliver the structured initialiser syntax, and get back to the problem with ambiguous instructions.

https://github.com/llvm/llvm-project/pull/70334