RFR: 8338814: [PPC64] Unify interface of cmpxchg for different types

[Lutz Schmidt]

On Fri, 23 Aug 2024 09:58:21 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

> PPC64 code has very complicated cmpxchg functions in MacroAssembler. We should have at least a unified argument list for the different types and the features should be usable with all types.
> I have also cleaned up the `RegisterOrConstant` functions because they are used by the cmpxchg code.
> 
> One difference in the argument list still exists: `cmpxchgb` and `cmpxchgh` use extra temp registers to support older processors. They should get removed with [JDK-8331859](https://bugs.openjdk.org/browse/JDK-8331859).

Changes  look good to me. 
I like uniform interfaces! Thanks for all the tedious work.

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Marked as reviewed by lucy (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/20689#pullrequestreview-2257020158