1-3% faster encoding optimizing SSE_NxN functions
1-3% faster encoding optimizing SSE_NxN functions

got rid of the |a-b|^|b-a| method and went back
to just (a-b)^2 instead.

quality | size(bytes) after/before | time (ms) after/before

Change-Id: Ia3e0e6507b3f903deb1e182f78dad6df07380fd0

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