haven: Introduce a memory sharing notification framework

Supplement the existing Haven memory resource notification
interface with a framework that can be used to dispatch
notifications about memory resources being shared/released
to the resource owners.

Change-Id: Ibbc14f4b29d68ffb1a9d6b035c79867783872225
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>