dm vdo: add basic hash map data structures

This patch adds two hash maps, one keyed by integers, the other by
pointers, and also a priority heap. The integer map is used for locking of
logical and physical addresses. The pointer map is used for managing
concurrent writes of the same data, ensuring that those writes are
deduplicated. The priority heap is used to minimize the search time for
free blocks.

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>
Signed-off-by: Matthew Sakai <msakai@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>