[CFL] Support for skip_chroma_rd in CB4X4

CFL is disabled when skip_chroma_rd is enabled. This is done by reusing
the logic in CB4X4. To facilitate integration, the skip logic used in CfL is
moved inside the read/write functions.

Results on Subset1:
master@2017-05-08T19:54:48.196Z -> cfl_baseline@2017-05-08T20:06:55.292Z
  PSNR |  PSNR Cb |  PSNR Cr | PSNR HVS |   SSIM | MS SSIM | CIEDE 2000
0.2668 | -12.0951 | -10.4138 |   0.3095 | 0.2998 |  0.2831 |    -3.6579
https://arewecompressedyet.com/?job=master%402017-05-08T19%3A54%3A48.196Z&job=cfl_baseline%402017-05-08T20%3A06%3A55.292Z

Change-Id: I45644baa1aceef5ad4da3332fcb10f3fbaac052b
3 files changed