fs: aio: convert to ring_folios and internal_folios

Since aio use folios in most functions, convert ring/internal_pages
to ring/internal_folios, let's directly use folio instead of page
throughout aio to remove hidden calls to compound_head(), eg,
flush_dcache_page().

Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Link: https://lore.kernel.org/r/20240321131640.948634-4-wangkefeng.wang@huawei.com


Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>