dm kcopyd: add sequential write feature

When copyying blocks to host-managed zoned block devices, writes must be
sequential.  However, dm_kcopyd_copy() does not guarantee this as writes
are issued in the completion order of reads, and reads may complete out
of order despite being issued sequentially.

Fix this by introducing the DM_KCOPYD_WRITE_SEQ feature flag.  This can
be specified when calling dm_kcopyd_copy() and should be set
automatically if one of the destinations is a host-managed zoned block
device.  For a split job, the master job maintains the write position at
which writes must be issued.  This is checked with the pop() function
which is modified to not return any write I/O sub job that is not at the
correct write position.

When DM_KCOPYD_WRITE_SEQ is specified for a job, errors cannot be
ignored and the flag DM_KCOPYD_IGNORE_ERROR is ignored, even if
specified by the user.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Bart Van Assche <bart.vanassche@sandisk.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>