Simplify context identification for coding ref frames

This patch simply aggregates the checking on the counts of certain
reference frames in the neighboring above and left blocks. It does
not incur any coding performance change.

Change-Id: I59a962ba95e7ab16731ce97371ec5709a582a0ba
diff --git a/av1/common/blockd.h b/av1/common/blockd.h
index 5c5d91c..2a82927 100644
--- a/av1/common/blockd.h
+++ b/av1/common/blockd.h
@@ -617,6 +617,10 @@
   CANDIDATE_MV ref_mv_stack[MODE_CTX_REF_FRAMES][MAX_REF_MV_STACK_SIZE];
   uint8_t is_sec_rect;
 
+  // Counts of each reference frame in the above and left neighboring blocks.
+  // NOTE: Take into account both single and comp references.
+  uint8_t neighbors_ref_counts[TOTAL_REFS_PER_FRAME];
+
   FRAME_CONTEXT *tile_ctx;
   /* Bit depth: 8, 10, 12 */
   int bd;