futher decouple DAX from block devices

[Christoph Hellwig]

Hi Dan,

this series cleans up and simplifies the association between DAX and block
devices in preparation of allowing to mount file systems directly on DAX
devices without a detour through block devices.

Diffstat:
 drivers/dax/Kconfig          |    4 
 drivers/dax/bus.c            |    2 
 drivers/dax/super.c          |  220 +++++--------------------------------------
 drivers/md/dm-linear.c       |   51 +++------
 drivers/md/dm-log-writes.c   |   44 +++-----
 drivers/md/dm-stripe.c       |   65 +++---------
 drivers/md/dm-table.c        |   22 ++--
 drivers/md/dm-writecache.c   |    2 
 drivers/md/dm.c              |   29 -----
 drivers/md/dm.h              |    4 
 drivers/nvdimm/Kconfig       |    2 
 drivers/nvdimm/pmem.c        |    9 -
 drivers/s390/block/Kconfig   |    2 
 drivers/s390/block/dcssblk.c |   12 +-
 fs/dax.c                     |   13 ++
 fs/erofs/super.c             |   11 +-
 fs/ext2/super.c              |    6 -
 fs/ext4/super.c              |    9 +
 fs/fuse/Kconfig              |    2 
 fs/fuse/virtio_fs.c          |    2 
 fs/xfs/xfs_super.c           |   54 +++++-----
 include/linux/dax.h          |   30 ++---
 22 files changed, 185 insertions(+), 410 deletions(-)