NEON functions for lossless coding

Verified OK, but right now they don't seem faster.
So they are disabled behind a USE_INTRINSICS flag (off for now)

Change-Id: I72a1c4fa3798f98c1e034f7ca781914c36d3392c
MIPS: MIPS32r1: Added optimizations for FastLog2

Functions VP8LFastLog2Slow and VP8LFastSLog2Slow

also: replaced some "% y" by "& (y-1)" in the C-version
(since y is a power-of-two)

Change-Id: I875170384e3c333812ca42d6ce7278aecabd60f0
Merge "MIPS: MIPS32r1: Added optimizations for FastLog2"