- shost->my_devices is gone and replaced by ->__devices, which is not
    exposed to drivers and locked by the host lock.  Use the exported
    helpers that do proper refcounting to access it.
  - sdev->access_count is gone as a side-effect, the sg interfaces
    to export it now return 1 for a present scsi_device.
  - drivers/scsi/host.h is empty now.