haven: Add support for MEM_NOTIFY

MEM_NOTIFY is useful for sending VMs notifications about
memory that has been shared with them, as well as sending
owners of memory an indication that a VM has released memory
that they own, so add support for it.

Change-Id: I65bf0d000c8b3850f04c85eec70692728314b26d
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>