[CFL] Add CfL Alpha cost to RDO

The cost of signaling the alpha symbol and the signs are added to the
DC_PRED rate in RDO.

Results on Subset1(compared to f9e04152b with CfL enabled)

   PSNR | PSNR Cb | PSNR Cr | PSNR HVS |    SSIM | MS SSIM | CIEDE 2000
-0.3699 |  1.5330 |  0.8664 |  -0.2881 | -0.3107 | -0.2587 |     0.1954

Change-Id: Icd9827d11ee4ef29dfb527e636f0f380bcafa062
diff --git a/av1/encoder/rdopt.c b/av1/encoder/rdopt.c
index b3e517e..201c598 100644
--- a/av1/encoder/rdopt.c
+++ b/av1/encoder/rdopt.c
@@ -5326,7 +5326,7 @@
   PALETTE_MODE_INFO *const pmi = &mbmi->palette_mode_info;
 #endif  // CONFIG_PALETTE
 
-  for (int mode_idx = DC_PRED; mode_idx < INTRA_MODES; ++mode_idx) {
+  for (int mode_idx = 0; mode_idx < INTRA_MODES; ++mode_idx) {
     int this_rate;
     RD_STATS tokenonly_rd_stats;
     PREDICTION_MODE mode = intra_rd_search_mode_order[mode_idx];
@@ -5361,6 +5361,11 @@
     this_rate =
         tokenonly_rd_stats.rate + cpi->intra_uv_mode_cost[mbmi->mode][mode];
 
+#if CONFIG_CFL
+    if (mode == DC_PRED) {
+      this_rate += xd->cfl->costs[mbmi->cfl_alpha_idx];
+    }
+#endif
 #if CONFIG_EXT_INTRA
     if (is_directional_mode && av1_use_angle_delta(mbmi->sb_type)) {
       this_rate += write_uniform_cost(2 * MAX_ANGLE_DELTA + 1,