Add config flag for mrc based transform experiment

Change-Id: I2d688d21de4a1d180f8ac36bb0363b57be55c0af
diff --git a/configure b/configure
index af13ac1..fe8d088 100755
--- a/configure
+++ b/configure
@@ -332,6 +332,7 @@
     ncobmc_adapt_weight
     bgsprite
     var_tx_no_tx_mode
+    mrc_tx
 "
 CONFIG_LIST="
     dependency_tracking