nilfs2: convert persistent object allocator to use kmap_local

nilfs2: convert persistent object allocator to use kmap_local

Regarding the allocator code that is commonly used in the ondisk inode
metadata file ifile and the disk address translation metadata file DAT,
convert the parts that use the deprecated kmap_atomic() and kmap() to use
kmap_local.

Most can be converted directly, but only
nilfs_palloc_prepare_alloc_entry() needs to be rewritten to change mapping
sections so that multiple kmap_local/kunmap_local calls are nested and
disk I/O can be avoided within the mapping sections.

Link: https://lkml.kernel.org/r/20240122140202.6950-7-konishi.ryusuke@gmail.com
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>