[PATCH v4 1/1] riscv: Add RVV memset via multiarch/IFUNC

[Yao Zihong]

Hi all,

Checked the intended semantics of hwprobe, AT_HWCAP and prctl
with Andy Chiu on the kernel Bugzilla [1]. The kernel-side clarification is:
- hwprobe reports per-CPU presence of RVV,  
- while AT_HWCAP and prctl(PR_RISCV_V_GET_CONTROL) report per-process
  availability.

So hwprobe is intentionally not equivalent to AT_HWCAP, and it is expected
that hwprobe will continue to report RVV even when a process has RVV disabled
via prctl().

Given this clarification, and earlier discussion agreed that the
prctl-disabled-RVV corner case should not block this minimal pilot for RVV
memset, would proceeding with v4 as-is(presence-only resolver) be acceptable?

[1] https://bugzilla.kernel.org/show_bug.cgi?id=220795

Thanks,
Zihong