Make 4-tap interp filter coefficients even numbers
Make 4-tap interp filter coefficients even numbers

This CL modified 4-tap interp filter coefficients to be even numbers,
which would help in writing 4-tap filter SIMD optimizations. The coding
performance change was negligible. Speed 1 borg test showed:
        avg_psnr:  ovr_psnr:    ssim:
lowres:  -0.003    -0.012      -0.017
midres:  0.029     0.018        0.043
hdres:   0.024     0.044        0.033

Change-Id: Id7c54bb9a9c1aee19c41bc6f1dc3b9682d158bba

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