dm crypt: add big-endian variant of plain64 IV

dm crypt: add big-endian variant of plain64 IV

The big-endian IV (plain64be) is needed to map images from extracted
disks that are used in some external (on-chip FDE) disk encryption
drives, e.g.: data recovery from external USB/SATA drives that support
"internal" encryption.

Signed-off-by: Milan Broz <gmazyland@gmail.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
(cherry picked from commit 7e3fd855ad66ffc0dd926911da23dd21e59f9462)
Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>
Tested-by: Qiang Wang <qiang.z.wang@oracle.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Orabug: 28043932
Signed-off-by: Brian Maly <brian.maly@oracle.com>
Conflicts:
	drivers/md/dm-crypt.c

Signed-off-by: Brian Maly <brian.maly@oracle.com>