LU-8066 obd: cleanup server sysfs symlinks handling

LU-8066 obd: cleanup server sysfs symlinks handling

Rename class_setup_tunables() to class_add_symlinks(). Move all the
special sysfs and debugfs symlink handling into the function
class_add_symlinks(). Now that the obd_type is created using sysfs
handling we can complete the initializion if the real obd device is
registered later. For example if lod is registered first and it
creates the the "lov" obd_type. Then if the lov module is loaded
later then class_register_type() will use the "lov" obd_type created
by the lod module.

Change-Id: I754ec15a88458b170422b988d783efbe20141b87
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-on: https://review.whamcloud.com/34715
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Petros Koutoupis <pkoutoupis@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>