mm/mm_init.c: move set_pageblock_order() to free_area_init()

pageblock_order only needs to be set once, there is no need to initialize
it in every zone/node.

Link: https://lkml.kernel.org/r/20230601063536.26882-1-haifeng.xu@shopee.com


Signed-off-by: Haifeng Xu <haifeng.xu@shopee.com>
Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>