fscrypt API cleanups v3

Hi all,

this series cleans up various fscrypt APIs to pass logical offsets in
and lengths in bytes, and on-disk sectors as 512-byte sector units,
like most of the VFS and block code.

Changes since v2:
 - use the local bio variable in io_submit_init_bio
 - use folio instead of io_folio (and actually test the noinline mode,
   which should have cought this for the last round)
 - add an extra IS_ENABLED(CONFIG_FS_ENCRYPTION) to safeguard
   against potentially stupid compilers
 - document the byte length needs to be a multiple of the block
   size
 - case to u64 when passing the byte length
 - move a hunk to an earlier patch
Changes since v1:
 - remove all buffer_head helpers, and do that before the API cleanups
   to simplify the series
 - fix a bisection hazard
 - spelling fixes in the commit logs
 - use "file position" to describe the byte offset into an inode
 - add another small ext4 cleanup at the end

Diffstat:
 fs/buffer.c                 |   18 ++++++++-
 fs/crypto/bio.c             |   40 +++++++++-----------
 fs/crypto/fscrypt_private.h |    3 -
 fs/crypto/inline_crypt.c    |   86 ++++----------------------------------------
 fs/crypto/keysetup.c        |    2 -
 fs/ext4/inode.c             |    5 ++
 fs/ext4/page-io.c           |   28 ++++++++++----
 fs/ext4/readpage.c          |   10 ++---
 fs/f2fs/data.c              |    7 ++-
 fs/f2fs/file.c              |    4 +-
 fs/iomap/direct-io.c        |    6 +--
 include/linux/fscrypt.h     |   37 ++++--------------
 12 files changed, 92 insertions(+), 154 deletions(-)