simplify the mdev interface v3

[Christoph Hellwig]

Hi all,

this series signigicantly simplies the mdev driver interface by following
the patterns for device model interaction used elsewhere in the kernel.

Changes since v2:
 - rebased to vfio/next
 - fix a pre-existing memory leak in i915 instead of making it worse
 - never manipulate if ->available_instances if drv->get_available is
   provided
 - keep a parent reference for the mdev_type
 - keep a few of the sysfs.c helper function around
 - improve the documentation for the parent device lifetime
 - minor spellig / formatting fixes

Changes since v1:
 - embedd the mdev_parent into a different sub-structure in i916
 - remove headers now inclued by mdev.h from individual source files
 - pass an array of mdev_types to mdev_register_parent
 - add additional patches to implement all attributes on the
   mdev_type in the core code

Diffstat:
 Documentation/driver-api/vfio-mediated-device.rst |   26 +--
 Documentation/s390/vfio-ap.rst                    |    2 
 Documentation/s390/vfio-ccw.rst                   |    2 
 drivers/gpu/drm/i915/gvt/gvt.h                    |    6 
 drivers/gpu/drm/i915/gvt/kvmgt.c                  |  158 ++++--------------
 drivers/gpu/drm/i915/gvt/vgpu.c                   |   66 ++-----
 drivers/s390/cio/cio.h                            |    4 
 drivers/s390/cio/vfio_ccw_drv.c                   |    3 
 drivers/s390/cio/vfio_ccw_ops.c                   |   60 +------
 drivers/s390/cio/vfio_ccw_private.h               |    2 
 drivers/s390/crypto/vfio_ap_ops.c                 |   68 +-------
 drivers/s390/crypto/vfio_ap_private.h             |    6 
 drivers/vfio/mdev/mdev_core.c                     |  185 ++++-----------------
 drivers/vfio/mdev/mdev_driver.c                   |    7 
 drivers/vfio/mdev/mdev_private.h                  |   32 ---
 drivers/vfio/mdev/mdev_sysfs.c                    |  187 +++++++++++-----------
 include/linux/mdev.h                              |   77 ++++-----
 samples/vfio-mdev/mbochs.c                        |  103 +++---------
 samples/vfio-mdev/mdpy.c                          |  115 +++----------
 samples/vfio-mdev/mtty.c                          |   94 +++--------
 20 files changed, 380 insertions(+), 823 deletions(-)