Refactor get_sign_bit_cost
Refactor get_sign_bit_cost

Change-Id: I646e93abb1064d05bac625ba4c567d377b249367

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