[SCSI] scsi_transport_spi: Export host width and HBA id

Currently it's impossible to find out if the host supports
wide SCSI unless you're committed to trawl through syslog.
And it's near impossible to find the actual HBA id, which
is settable for some SCSI HBAs (like aic7xxx).
So export them via sysfs.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Ankit Jain <jankit@suse.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>