msm: camera: Allow user to abort live snapshot.

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>