board: 8960: Make the ion multimedia heap reusable

Mark the ion multimedia heap used by camera and video as
reusable. When no memory is allocated from this heap,
the pages are available for use by the system. The memory
is made available as soon as the first Ion allocation occurs.

Change-Id: I66df78d20e797647ca8b866d3fe60bd683742983
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>