scsi: target: tcm_fc: Convert to new submission API

target_submit_cmd() is now only for simple drivers that do their own sync
during shutdown and do not use target_stop_session().

tcm_fc uses target_stop_session() to sync session shutdown with LIO core,
so we use target_init_cmd(), target_submit_prep(), target_submit(), because
target_init_cmd() will now detect the target_stop_session() call and return
an error.

Link: https://lore.kernel.org/r/20210227170006.5077-14-michael.christie@oracle.com
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>