rt: mm/page_alloc: backport missing bits from __build_all_zonelists() fix

A while ago upstream landed commit a2ebb51575828 ("mm/page_alloc: use
write_seqlock_irqsave() instead write_seqlock() + local_irq_save().")
to fix a problem that had already been worked on v5.10-rt via commit
7bdd3bd5143a4 ("Revert "mm/page_alloc: fix potential deadlock on
zonelist_update_seqseqlock""). Sebastian pointed out it was important
to backport the missing elements of a2ebb51575828 for code consistency.

Fixes: 7bdd3bd5143a4 ("Revert "mm/page_alloc: fix potential deadlock on zonelist_update_seqseqlock"")
Cc: stable-rt@vger.kernel.org
Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>