Yes, this is the patch every maintainer of a modern HBA waited for the
last years </shameless plug>.

With all my recent changes there's no more reason to call scsi_register_host
except for the intialization it performs to every host found in
scsi_register.  But a driver can aswell do that at the end of it's
per-HBA detection routine (i.e. in ->probe for a modern PCI driver), so
export that code as scsi_add_host to drivers.  Do the same for the
release path (scsi_remove_host).  Such a new-style driver needs neither
->detect or ->release and is in theory hotplug-capable (well, once all
the races in the scsi midlayer are fixed..)