Refactor get_entropy_contexts_plane() block step count
Refactor get_entropy_contexts_plane() block step count

Make this scalable to minimum transform block size.

Change-Id: I13b0ac841df4e87e6c6bcd8be358d817b4be4328

luctrudeau/aom,smarter/aom,smarter/aom,mbebenita/aom,smarter/aom,GrokImageCompression/aom,mbebenita/aom,smarter/aom,luctrudeau/aom,mbebenita/aom,mbebenita/aom,luctrudeau/aom,mbebenita/aom,mbebenita/aom,smarter/aom,GrokImageCompression/aom,GrokImageCompression/aom,luctrudeau/aom,GrokImageCompression/aom,GrokImageCompression/aom,mbebenita/aom,mbebenita/aom,luctrudeau/aom,mbebenita/aom,luctrudeau/aom,GrokImageCompression/aom,smarter/aom