Drain the command queue and place all commands on a completion list.
Perform command completion on that list outside the host/queue locks.
Further, move purged command compeletions outside the host_lock as well.

Link: https://lore.kernel.org/r/20210106201835.1053593-5-tyreld@linux.ibm.comReviewed-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: Tyrel Datwyler <tyreld@linux.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>