[CFL] UV_PREDICTION_MODE

A separate prediction mode struct is added to allow
for uv-only modes (like CfL). Note: CfL will be
added as a separate mode in an upcoming commit.

Results on Subset1 (Compared to 4266a7ed with CfL enabled)
  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: Ie80711c641c97f745daac899eadce6201ed97fcc
diff --git a/av1/encoder/encodeframe.c b/av1/encoder/encodeframe.c
index ae19b69..ab1218a 100644
--- a/av1/encoder/encodeframe.c
+++ b/av1/encoder/encodeframe.c
@@ -5662,8 +5662,8 @@
   const MB_MODE_INFO *const mbmi = &mi->mbmi;
 #if CONFIG_ENTROPY_STATS
   const PREDICTION_MODE y_mode = mbmi->mode;
-  const PREDICTION_MODE uv_mode = mbmi->uv_mode;
-#else
+  const UV_PREDICTION_MODE uv_mode = mbmi->uv_mode;
+#else   // CONFIG_ENTROPY_STATS
   (void)counts;
   (void)above_mi;
   (void)left_mi;
@@ -5710,7 +5710,7 @@
           mbmi->filter_intra_mode_info.use_filter_intra_mode[0];
       ++counts->filter_intra[0][use_filter_intra_mode];
     }
-    if (mbmi->uv_mode == DC_PRED
+    if (mbmi->uv_mode == UV_DC_PRED
 #if CONFIG_CB4X4
         &&
         is_chroma_reference(mi_row, mi_col, bsize, xd->plane[1].subsampling_x,