[sparkplug] Make --sparkplug readonly on unsupported archs

Bug: v8:11420
Change-Id: I41eda774ba31a25b7f199ffea7f97fca9c44835e
Fixed: chromium:1179650
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2704670


Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72861}