Re-schedule sub8x8 chroma component encoding process

Use the top-left 4x4 luma block's coding information for chroma
component encoding at size 4x4.

Change-Id: I4bcfbc2bf8b71f7fc30094553503468460a56f9b
diff --git a/av1/common/onyxc_int.h b/av1/common/onyxc_int.h
index fbe9400..bab2a29 100644
--- a/av1/common/onyxc_int.h
+++ b/av1/common/onyxc_int.h
@@ -719,6 +719,12 @@
 #endif  // CONFIG_EXT_PARTITION_TYPES
 }
 
+#if CONFIG_CB4X4
+static INLINE int is_chroma_reference(const int mi_row, const int mi_col) {
+  return !((mi_row & 0x01) || (mi_col & 0x01));
+}
+#endif
+
 #if CONFIG_EXT_PARTITION_TYPES
 static INLINE void update_ext_partition_context(MACROBLOCKD *xd, int mi_row,
                                                 int mi_col, BLOCK_SIZE subsize,