[riscv64] Use macros to control the compilation of RVV

Change-Id: Iac021f8666058042f5c26cf07d0f3810a1d451fc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3528374


Auto-Submit: Yahan Lu <yahan@iscas.ac.cn>
Reviewed-by: ji qiu <qiuji@iscas.ac.cn>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Yahan Lu <yahan@iscas.ac.cn>
Cr-Commit-Position: refs/heads/main@{#79617}