The probabilities and CDFs were tuned using aom_entropy_optimizer tool.

midres: -0.062 overall PSNR, -0.100 on SSIM
(but significant gain on Keiba_832x480_30.y4m clip:
-1.331 on overall PSNR and -1.903 on SSIM)
lowres: +0.013 on overall PSNR, -0.062 on SSIM

Change-Id: Ie143a3914ef45939c8744ff6b2ed9f1d0a59353e