erofs: enable large folios for iomap mode

erofs: enable large folios for iomap mode

Enable large folios for iomap mode.  Then the readahead routine will
pass down large folios containing multiple pages.

Let's enable this for non-compressed format for now, until the
compression part supports large folios later.

When large folios supported, the iomap routine will allocate iomap_page
for each large folio and thus we need iomap_release_folio() and
iomap_invalidate_folio() to free iomap_page when these folios get
reclaimed or invalidated.

Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20221130060455.44532-1-jefflexu@linux.alibaba.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>