haven: Add support for MEM_SHARE/MEM_LEND

Relying on hyp_assign for sharing memory is not sufficient,
as there are certain cases where hyp_assign is not applicable
for sharing memory (e.g. I/O memory). Add support for the MEM_SHARE
and MEM_LEND operations for sharing/lending memory with other
VMs respectively.

Change-Id: I7de502385a045f073540fa30c164b3410f6b5bd0
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>