scsi: scsi: Export blacklist flags to sysfs

Each scsi device is scanned according to the found blacklist flags, but
this information is never presented to sysfs.  This makes it quite hard
to figure out if blacklisting worked as expected.  With this patch we're
exporting an additional attribute 'blacklist' containing the blacklist
flags for this device.

Signed-off-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>