haven: Add support for the MEM_ACCEPTED notification

It's useful for other virtual machines (VMs) to know if another
VM has successfully received a resource that was shared with it
(e.g. state tracking can be controlled better with this sort of
information). Add support for the MEM_ACCEPTED notification, which
clients can use to notify the VM that owns the resource that was
shared with it that it has accepted the resource and is using it.
Also, add support in the mem-notifier driver to forward the
MEM_ACCEPTED notification to clients.

Change-Id: I05b9f1d37906d7c2aa729b97df2f8ceb78b560bd
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>