mm/page_alloc: use str_off_on() helper in build_all_zonelists()

Remove hard-coded strings by using the str_off_on() helper function.

Link: https://lkml.kernel.org/r/20241021091340.5243-2-thorsten.blum@linux.dev


Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>