Limit inter mode context dependency scope
Limit inter mode context dependency scope

Constrain the zeromv context model to depend on the top-left
8x8 block in the collocated region only. This reduces the latency
on parsing its context index. The coding performance loss is around
0.05% level.

Change-Id: I29bc7e4eb3e7c2e4ab32acd071420f4cb038c856

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom