This allows a mdev driver to opt out of using vfio_mdev.c, instead the
driver will provide a 'struct mdev_driver' and register directly with the
driver core.

Much of mdev_parent_ops becomes unused in this mode:
- create()/remove() are done via the mdev_driver probe()/remove()
- mdev_attr_groups becomes mdev_driver driver.dev_groups
- Wrapper function callbacks are replaced with the same ones from
  struct vfio_device_ops
Signed-off-by: NJason Gunthorpe <jgg@nvidia.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NCornelia Huck <cohuck@redhat.com>
Reviewed-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: NKirti Wankhede <kwankhede@nvidia.com>
Link: https://lore.kernel.org/r/20210617142218.1877096-8-hch@lst.deSigned-off-by: NAlex Williamson <alex.williamson@redhat.com>