The place where av1_daala_dist() is applied for sub8x8 partition is
moved from sub8x8 mode decision functions to rd_pick_partition().

BD-Rate change by daala-dist with '--disable-var-tx' is:
(AWCY, objective-1-fast, high delay mode)

   PSNR | PSNR Cb | PSNR Cr | PSNR HVS |    SSIM | MS SSIM | CIEDE 2000
15.1558 | 12.9585 | 14.4662 |  -3.8651 | -1.7102 | -9.2956 |    10.8686

In MSE probe mode:

  PSNR | PSNR Cb | PSNR Cr | PSNR HVS |   SSIM | MS SSIM | CIEDE 2000
0.0429 |  0.0435 |  0.1651 |  -0.0415 | 0.0850 |  0.0122 |     0.0546

Change-Id: I3b2ea916d41c48e433eb641adf44552e4725c198