Add a helper function exportBuffers in DmaBufAllocator to make it easier to use. It'll be used in Virtual Pipeline Handler and SoftwareIsp. Signed-off-by: Harvey Yang <chenghaoyang@chromium.org> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com> Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com> Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>