scsi: ibmvscsi: add vscsi hosts to global list_head

Add each vscsi host adatper to a new global list_head named
ibmvscsi_head. There is no functional change. This is meant primarily as
a convience for locating adapters from within the debugger or crash
utility.

[mkp: fixed typo]

Signed-off-by: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>