This CL separates checks for hardware support from checks for software
configuration. We unconditionally allocate a protection key to know
whether hardware support is there, but then only use it if PKU is
enabled via flags.
This will allow us to collect statistics on hardware availability even
if PKU cannot be used yet on ChromeOS. Allocation should always be fine,
and has been finched for several weeks now. The remaining kernel issue
on ChromeOS does not affect allocation and deallocation of protection
keys, so it is safe to unconditionally enable that.

R=ahaas@chromium.org

Bug: v8:11974
Change-Id: I62fd48e6302aecae9843a62861d978f86ea52141
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3315446
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78258}