Due to some reason, user can decide to abort a live snapshot while it is in progress. Add support to stop the VFE write masters right away so that the VFE stops writing on the buffers allocated by the user. Also send an ACK message to userspace once we get confirmation from VFE that it has stopped using the buffers. CRs-Fixed: 373080 Change-Id: Ia4d9134298dd3a1a51f5829f9bcc2b80d6f21d0f Signed-off-by: Kiran Kumar H N <hurlisal@codeaurora.org>