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

arch/x86/mm/pat/set_memory.c

@@ -587,10 +587,6 @@ static inline pgprot_t verify_rwx(pgprot_t old, pgprot_t new, unsigned long star
 {
 	unsigned long end;
 
-	/* Kernel text is rw at boot up */
-	if (system_state == SYSTEM_BOOTING)
-		return new;
-
 	/*
 	 * 32-bit has some unfixable W+X issues, like EFI code
 	 * and writeable data being in the same page.  Disable