scsi: mpt3sas: wait for and flush running commands on shutdown/unload

commit c666d3be99c000bb889a33353e9be0fa5808d3de upstream.

This patch finishes all outstanding SCSI IO commands (but not other commands,
e.g., task management) in the shutdown and unload paths.

It first waits for the commands to complete (this is done after setting
'ioc->remove_host = 1 ', which prevents new commands to be queued) then it
flushes commands that might still be running.

This avoids triggering error handling (e.g., abort command) for all commands
possibly completed by the adapter after interrupts disabled.

[mauricfo: introduced something in commit message.]

Signed-off-by: Sreekanth Reddy <sreekanth.reddy@broadcom.com>
Tested-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
[mauricfo: backport to linux-4.14.y (a few updates to context lines)]
Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>