Refactor tile_worker_hook function
Refactor tile_worker_hook function

Extracted fragments of code in tile_worker_hook
function into separate functions to facilitate
row based decoder multi-threading.

Change-Id: I0c1fc0a2c077f3559e71b044b8f9531eddec112a

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