nilfs2: convert segment usage file to be folio-based

For the sufile, which is a metadata file that holds information about
managing segments, convert the page-based implementation to a folio-based
implementation.

kmap_local_page() is changed to use kmap_local_folio(), and where offsets
within a page are calculated using bh_offset(), are replaced with
calculations using offset_in_folio() with an additional helper function
nilfs_sufile_segment_usage_offset().

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ryusuke Konishi <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: konis