dm: add presuspend_undo hook to target_type

The DM thin-pool target now must undo the changes performed during
pool_presuspend() so introduce presuspend_undo hook in target_type.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Acked-by: Joe Thornber <ejt@redhat.com>

diff --cc drivers/md/dm-table.c
Simple merge

diff --cc drivers/md/dm.c
Simple merge

diff --cc drivers/md/dm.h
Simple merge

diff --cc include/linux/device-mapper.h
Simple merge

diff --cc include/uapi/linux/dm-ioctl.h
Simple merge