Add adapt_scan experimental flag

Change-Id: I1424690fa792b960a1cfb78bbcb37da6b9899ee6
diff --git a/configure b/configure
index 7901ef3..99d2bb8 100755
--- a/configure
+++ b/configure
@@ -287,6 +287,7 @@
     cb4x4
     frame_size
     delta_q
+    adapt_scan
 "
 CONFIG_LIST="
     dependency_tracking