scsi: target: Add default fabric ops callouts

There are several callouts in target fabric ops that most of fabric drivers
fill with a function returning the same value.

Stop requiring such callouts to exist in the ops, fill them in TCM Core.

Signed-off-by: Dmitry Bogdanov <d.bogdanov@yadro.com>
Link: https://lore.kernel.org/r/20230313181110.20566-2-d.bogdanov@yadro.com


Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>