[CFL] New UV_PREDICTION_MODE for CFL

CfL is now an independent mode.

Results on Subset1 (Compared to 4266a7ed with CFL enabled)

   PSNR | PSNR Cb | PSNR Cr | PSNR HVS |    SSIM | MS SSIM | CIEDE 2000
-0.1645 | -0.4017 |  0.2475 |  -0.1851 | -0.2179 | -0.2338 |    -0.2897

Change-Id: I2e86e7ea7bfc12bb1d763e70a136ca992d57a3c5
diff --git a/av1/common/blockd.h b/av1/common/blockd.h
index 0b428cd..b565d5f 100644
--- a/av1/common/blockd.h
+++ b/av1/common/blockd.h
@@ -518,6 +518,7 @@
 #endif              // CONFIG_SMOOTH_HV
 #endif              // CONFIG_ALT_INTRA
     TM_PRED,        // UV_TM_PRED
+    DC_PRED,        // CFL_PRED
   };
   return uv2y[mode];
 }