Refactor reset_skip_context() to support 2x2 txfm block
Refactor reset_skip_context() to support 2x2 txfm block

Refactor to remove the assumption that transform block operates in
the unit of 4x4. This generalizes the codec to support 2x2 transform
block later.

Change-Id: If1448a915f5765d409394c914af68f44b0749bc2

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