Use of temporal context for encoding delta updates.

Use of temporal context for encoding delta updates.

- Used three probability approach for temporal context as follows:
P0 - probability of no change if both above and left not changed
P1 - probability of no change if one of above and left has changed
P2 - probability of no change if both above and left have changed

In addition, a 1 bit/frame has been used to decide whether to use temporal context or to encode directly.  The cost of using both the schemes is calculated ahead and the temporal_update flag is set if the cost of using temporal context is lower than encoding the segment ids directly.

This approach has given around 20% reduction in cost of bits needed to encode segmentation ids.

Change-Id: I44a5509599eded215ae5be9554314280d3d35405