nilfs2: convert persistent object allocator to be folio-based

nilfs2: convert persistent object allocator to be folio-based

Regarding the persistent oject allocator, a common mechanism for
allocating objects in metadata files such as inodes and DAT entries,
convert the page-based implementation to a folio-based implementation.

In this conversion, helper functions nilfs_palloc_group_desc_offset() and
nilfs_palloc_bitmap_offset() are added and used to calculate the byte
offset within a folio of a group descriptor structure and bitmap,
respectively, to replace kmap_local_page with kmap_local_folio.

In addition, a helper function called nilfs_palloc_entry_offset() is
provided to facilitate common calculation of the byte offset within a
folio of metadata file entries managed in the persistent object allocator
format.

Link: https://lkml.kernel.org/r/20241024092602.13395-5-konishi.ryusuke@gmail.com
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>