staging: virthba driver to access shared SCSI hba

The virthba module provides access to a shared SCSI host bus adapter
and one or more disk devices, by proxying SCSI commands between the
guest and the service partition that owns the shared SCSI adapter,
using a channel between the guest and the service partition. The disks
that appear on the shared bus are defined by the s-Par configuration
and enforced by the service partition, while the guest driver handles
sending commands and handling responses. Each disk is shared as a
whole to a guest. Sharing the bus adapter in this way provides
resiliency; should the device encounter an error, only the service
partition is rebooted, and the device is reinitialized. This allows
guests to continue running and to recover from the error.

Signed-off-by: Ken Cox <jkc@redhat.com>
Cc: Ben Romer <sparmaintainer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>