ion : Expose ION API to query buffer VM information

Allow ION clients to be able to determine the VM information associated
with an ION buffer, such as the VMIDs it is assigned to as well as the
VM permissions.

Change-Id: Id0be0b505bc84beff373e4e2ae16b71ec4f09d43
Signed-off-by: Liam Mark <lmark@codeaurora.org>