riscv: hwprobe: Report Supm only when available

[Radim Krčmář]

2026-10-16T16:45:00-05:00, Andy Chiu <tchiu at tenstorrent.com>:
> On Tue, Oct 06, 2026 at 09:53:01AM +0200, Radim Krcmár wrote:
> >  ---
> >  The compat hiding and global sysctl toggle better fit in Andy's series.
>
>                                      That series was dropped because the
> mechanism was not in flavor of reviewers and we are going to deprecate
> the prctl[1]. But I can see there is still a need for understanding if an
> extension exists at runtime. We will take time to revisit that

Thanks for the review and clarification.

We could make the design cleaner without losing practical flexibility by
abandoning the sysctl knobs in favor of kernel command line parameters.

Boot time configuration would stabilize user-mode execution environment
and we wouldn't need to expand hwprobe now.  It's still breaking UABI,
through... I'll send a proposal for discussion after the merge window.