Speedup WebP lossless compression for low effort (m=0) mode with following:
- Disable Cross-Color transform.
- Evaluate predictors #11 (paeth), #12 and #13 only.

Change-Id: I857264c85c61c3957d4fb45ae32d261d947c8bed
MIPS: dspr2: added optimization for function ExportRowC

Change-Id: Ie1a303089eb64736f8bc7573819a8219aa7528a3
Merge "MIPS: dspr2: added optimization for function ExportRowC"
MIPS: dspr2: added optimization for function ImportRow

Change-Id: I8205b551755ee51f5efd0c54d64c8b09771786b1
replace unneeded calls to HistogramCopy() by swaps

most of the time, we don't need to actually move the
data.

Compression is randomly slightly different, because HistogramCompactBins() changed.
Timing is about the same.

Change-Id: Ia6af8e9780581014d6860f2b546189ac817cfad1
Merge "MIPS: dspr2: added optimization for function ImportRow"
method=0: Don't evaluate any predictor

and apply Paeth predictor (predictor#11) for the low effort (m=0) mode.

For 1000 image PNG corpus (m=0), this change yields speedup of 25% at lower quality
range and about 10% for higher quality range.

Change-Id: I0f036b8ffe45c241e63a067cbf01527b13d8de93