It's only called by mm_init(). Add __init annotations to it.

Link: https://lkml.kernel.org/r/20220916072257.9639-6-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Reviewed-by: NDavid Hildenbrand <david@redhat.com>
Reviewed-by: NAnshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: NOscar Salvador <osalvador@suse.de>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>