Cleaning up vp9_entropy.h file.

Renaming constants for consistency:
  DCT_VAL_CATEGORY1 => CATEGORY1_TOKEN
  DCT_VAL_CATEGORY2 => CATEGORY2_TOKEN
  DCT_VAL_CATEGORY3 => CATEGORY3_TOKEN
  DCT_VAL_CATEGORY4 => CATEGORY4_TOKEN
  DCT_VAL_CATEGORY5 => CATEGORY5_TOKEN
  DCT_VAL_CATEGORY6 => CATEGORY6_TOKEN
  DCT_EOB_TOKEN     => EOB_TOKEN
  DCT_EOB_MODEL_TOKEN => EOB_MODEL_TOKEN
  MAX_ENTROPY_TOKENS => ENTROPY_TOKENS

Moving constants:
  INTER_MODE_CONTEXTS from vp9_entropy.h to vp9_blockd.h.
  EOSB_TOKEN from vp9_entropy.h to vp9_tokenize.h

Change-Id: I5fcbf081318e1d365792b6d290a930c6cb0f3fc2