The function cfl_compute_parameters is added and contains the logic
related to building the CfL context parameters. As such, many cfl
functions can now be encapsulated inside of cfl.c and not exposed to the
rest of AV1.

This also allows for supplemental asserts that validate that the CfL
context is properly built.

Results on Subset1 (compared to 9c6f8547 with CfL)

  PSNR | PSNR Cb | PSNR Cr | PSNR HVS |   SSIM | MS SSIM | CIEDE 2000
0.0000 |  0.0000 |  0.0000 |   0.0000 | 0.0000 |  0.0000 |     0.0000

Change-Id: I6d14a426416b3af5491bdc145db7281b5e988cae