Optimize VP8SetResidualCoeffs.

Brings down WebP lossy encoding timings by 5%

Change-Id: Ia4a2fab0a887aaaf7841ce6d9ee16270d3e15489
strong filtering speed-up (~2-3% x86, ~1-2% for NEON)

Extract loop invariant and avoid storing/loading samples
if they can be re-used. This is particularly interesting when
a transpose is involved (HFilter16i).

Change-Id: I93274620f6da220a35025ff8708ff0c9ee8c4139
remove unused #include's

Change-Id: Icd91a4b6a0bde49145f57e3e74a997822c45792c
Merge "strong filtering speed-up (~2-3% x86, ~1-2% for NEON)"
Merge "remove unused #include's"