LU-18162 obdclass: init LU device after alloc

LU-18162 obdclass: init LU device after alloc

During obd_setup, ldto_device_alloc will be called if it
is defined. Initialize each lu device after it is allocated.
This isn't currently used by any existing LU device. This is
intended for future LU device conversions.

Test-Parameters: trivial
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: I859e467971db4335ae98fbc57643be8e1a261694
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/58784
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>