x86/mm: Do verify W^X at boot up

Straight up revert of commit:

  a970174d ("x86/mm: Do not verify W^X at boot up")

now that the root cause has been fixed.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20221025201058.011279208@infradead.org