rewrite Disto4x4 in enc_neon.c with intrinsic

Performance test:
Platform: A9
Input data: bryce.yuv  11158x2156
performance of assembly is the base. Less ratio is better.
|toolchain |assembly |intrinsic |
|gcc4.6    |100%     |97.15%    |
|gcc4.8    |100%     |95.51     |

Change-Id: Idc2446685acdeb58a4dbdcdae533c68a83a1b879
add lossless incremental decoding support

* We don't need to change DecodeAlpha, since incremental
decoding is not useful for Alpha (we already decode
progressively along the RGB)
* Similarly, we don't do incremental decoding for level>0 planes:
   the metadata don't turn into visible pixel (only the ones in level0), so...
(No visible speed change)

Change-Id: I2fd4b9ba227561a7dbede647686584b752be7baa
Merge "rewrite Disto4x4 in enc_neon.c with intrinsic"