dec_neon: add VE4 intra predictor

based on SSE2 version, ~59% faster

Change-Id: Iaa2181eb51bd975de0e9fe5c7b66ed18188f0e3b
dec_neon: add LD4 intra predictor

based on SSE2 version, ~55% faster

Change-Id: I782282ffc31dcf238890b3ba0decccf1d793dad0
dec_neon: add TM4 intra predictor

~21% faster

Change-Id: Ia9ed4ca650f9d544821fa1faf3173611806a272a
dec_neon: add DC4 intra predictor

~70% faster

Change-Id: I2e06907b8d69be71a8c5581832c931923c24bab0
Merge "dec_neon: add VE4 intra predictor"
Merge changes I2e06907b,Ia9ed4ca6,I782282ff

* changes:
  dec_neon: add DC4 intra predictor
  dec_neon: add TM4 intra predictor
  dec_neon: add LD4 intra predictor
Unify the API between VP8BitWriter and VP8LBitWriter

BitReader will be next...

Change-Id: Icd9e7ab2e3890131e664c0523627d9b8c5399a74