dm vdo: add the top-level DM target

dm vdo: add the top-level DM target

This adds the dm-vdo target.

The dm-vdo target provides inline deduplication, compression, and
zero-block elimination, allowing applications to consume less actual
storage than a normal target. By layering it with other device mapper
targets, it can add these features to any storage stack. It can also
provide a common deduplication pool for groups of targets. The vdo target
does not protect against data corruption, relying instead on integrity
protection of the storage below it.

Co-developed-by: J. corwin Coburn <corwin@hurlbutnet.net>
Signed-off-by: J. corwin Coburn <corwin@hurlbutnet.net>
Co-developed-by: Michael Sclafani <dm-devel@lists.linux.dev>
Signed-off-by: Michael Sclafani <dm-devel@lists.linux.dev>
Co-developed-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
Signed-off-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
Co-developed-by: Bruce Johnston <bjohnsto@redhat.com>
Signed-off-by: Bruce Johnston <bjohnsto@redhat.com>
Co-developed-by: Ken Raeburn <raeburn@redhat.com>
Signed-off-by: Ken Raeburn <raeburn@redhat.com>
Signed-off-by: Matthew Sakai <msakai@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>