[jdk21] RFR: 8309258: RISC-V: Add riscv_hwprobe syscall

[Fei Yang]

On Tue, 27 Jun 2023 06:55:44 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

> Hi all,
> 
> This pull request contains a backport of commit [31b6fd77](https://github.com/openjdk/jdk/commit/31b6fd775f1c4f2841d9a52ad5f275ad446ee661) from the [openjdk/jdk](https://git.openjdk.org/jdk) repository.
> 
> The commit being backported was authored by Robbin Ehn on 20 Jun 2023 and was reviewed by Feilong Jiang, Thomas Stuefe, Fei Yang and Ludovic Henry.
> 
> Thanks!

Marked as reviewed by fyang (Reviewer).

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PR Review: https://git.openjdk.org/jdk21/pull/67#pullrequestreview-1500363146