dsp: initialize VP8PredChroma8 in VP8DspInit()

the table becomes non-const to allow for platform-specific optimizations

Change-Id: I32d2b51480020dc653ecfafd20b6b0f096af349f
bit_reader/kVP8NewRange: range_t -> uint8_t

decreases the size of each entry from 4 bytes to 1.

Change-Id: I3e6a50bcbc279e5edfa411edb97b04300dedc7ae
dec_neon: add TM8uv

~68% faster

reuses TM4() adding support for the additional rows, the columns were
already being done.

Change-Id: I6eac17e58cd1c636082bf7281f70f884ec399a6b
Merge changes I6eac17e5,I32d2b514

* changes:
  dec_neon: add TM8uv
  dsp: initialize VP8PredChroma8 in VP8DspInit()