scsi: core: host template attribute groups

The patch introduces an additional field in the scsi_host_template
structure - struct attribute_group **sdev_group.  This field allows to
define groups of attributes. It will provide an ability to use binary
attributes as well as device attributes and to group them under
subfolders if necessary.

Signed-off-by: Stanislav Nijnikov <stanislav.nijnikov@wdc.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>