Account for rectangular transform block sizes in lv-map ctx

Account for the rectangular transform block sizes in the non-zero
map context model.

Change-Id: I16cf21a4120c10c213df10950aeb4ef0ea40c477
diff --git a/av1/common/entropy.h b/av1/common/entropy.h
index ce9e406..e40e4a9 100644
--- a/av1/common/entropy.h
+++ b/av1/common/entropy.h
@@ -71,7 +71,7 @@
 #endif  // CONFIG_CTX1D
 
 #if CONFIG_EXT_TX
-#define SIG_COEF_CONTEXTS_2D 16
+#define SIG_COEF_CONTEXTS_2D 26
 #define SIG_COEF_CONTEXTS_1D 16
 #define SIG_COEF_CONTEXTS \
   (SIG_COEF_CONTEXTS_2D + SIG_COEF_CONTEXTS_1D + SIG_COEF_CONTEXTS_1D)