Reduce memory allocated to frame MODE_INFO
Reduce memory allocated to frame MODE_INFO

Instead of always adding 1 SB, this patch modified calc_mi_size(),
and adaptively assigned mi_size based on frame size. This reduced
the frame MODE_INFO memory.

Change-Id: If2fe8f89ad158341dc8b595148a772118147ff99

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