Add support preference libraries to docs build

b/22795957

Change-Id: Ia8e02fd7726102f524a16f2f84e9c2bdd4d37f8f
diff --git a/core/pathmap.mk b/core/pathmap.mk
index 59c9be2..4d9b069 100644
--- a/core/pathmap.mk
+++ b/core/pathmap.mk
@@ -117,7 +117,10 @@
         v17/leanback \
         design \
         percent \
-        recommendation
+        recommendation \
+        v7/preference \
+        v14/preference \
+        v17/preference-leanback
 
 #
 # A list of all source roots under frameworks/multidex.