add bvec initialization helpers

[Christoph Hellwig]

Hi all,

this series adds the helpers to initalize a bvec.  These remove open coding of
bvec internals and help with experimenting with other representations like
a phys_addr_t instead of page + offset.

Diffstat:
 block/bio-integrity.c             |    7 ------
 block/bio.c                       |   12 +----------
 drivers/block/rbd.c               |    7 ++----
 drivers/block/virtio_blk.c        |    4 ---
 drivers/block/zram/zram_drv.c     |   15 +++-----------
 drivers/nvme/host/core.c          |    4 ---
 drivers/nvme/target/io-cmd-file.c |   10 +--------
 drivers/nvme/target/tcp.c         |    5 +---
 drivers/scsi/sd.c                 |   36 ++++++++++++++++------------------
 drivers/target/target_core_file.c |   18 +++++------------
 drivers/vhost/vringh.c            |    5 +---
 fs/afs/write.c                    |    8 ++-----
 fs/ceph/file.c                    |   10 ++++-----
 fs/cifs/connect.c                 |    5 ++--
 fs/cifs/fscache.c                 |   16 +++++----------
 fs/cifs/misc.c                    |    5 +---
 fs/cifs/smb2ops.c                 |    6 ++---
 fs/coredump.c                     |    7 +-----
 fs/nfs/fscache.c                  |   16 +++++----------
 fs/orangefs/inode.c               |   22 ++++++--------------
 fs/splice.c                       |    5 +---
 include/linux/bvec.h              |   40 ++++++++++++++++++++++++++++++++++++++
 io_uring/rsrc.c                   |    4 ---
 mm/page_io.c                      |    8 +------
 net/ceph/messenger_v1.c           |    7 +-----
 net/ceph/messenger_v2.c           |   28 ++++++++++----------------
 net/rxrpc/rxperf.c                |    8 ++-----
 net/sunrpc/svcsock.c              |    7 +-----
 net/sunrpc/xdr.c                  |    5 +---
 29 files changed, 143 insertions(+), 187 deletions(-)