We already have a "scsi" hostdev subsys type, which refers to a single
LUN that is passed through to a guest.  But what of things where
multiple LUNs are passed through via a single SCSI HBA, such as with
the vhost-scsi target?  Create a new hostdev subsys type that will
carry this.
Signed-off-by: NEric Farman <farman@linux.vnet.ibm.com>