msm: camera: support exposure metering and HDR snapshots

With this change we achieve multiple things related
to correct HDR functionality. First, we do not
always configure ping and pong to be the same buffer in
case of the snapshot mode. This would help support taking
mulitple snapshots. Second, we support for logic to skip
frames in case of snapshot, a necessity for the exposure
metering feature. Third, we support post processing
divert of both snapshot and thumbnail buffers to be
taken from either mctl queue or video queue, to be
determined at runtime.

Change-Id: Ibcf2bbfc171b2686ca44e6366feadf435368fa5f
Signed-off-by: Ankit Premrajka <ankitp@codeaurora.org>