scsi: vhost-scsi: Report direction completion support

scsi: vhost-scsi: Report direction completion support

This has vhost-scsi report that it supports direct completions.

When using a worker task per queue or group of queues with fast backends
then enabling direct completion and submissions increases performance
20-30% with workloads like:

  fio --filename=/dev/sdb  --direct=1 --rw=randrw --bs=8K \
      --ioengine=libaio --iodepth=128  --numjobs=$jobs

As jobs matches and passes the number of vCPUs in the VM then the
benefit increases.

However, when using a single worker then queueing completions and
submissions is best as the worker is busy handling mapping data and
setting/tearing down commands.

Signed-off-by: Mike Christie <michael.christie@oracle.com>
Link: https://patch.msgid.link/20260222232946.7637-5-michael.christie@oracle.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>