Add build config for a bluetooth apex

Bug: 142747680
Test: compile
Change-Id: I72be6a6c90d0eaf2e763c6595664f3e4b9a8d4e0
diff --git a/Android.bp b/Android.bp
index c56d51d..113be7b 100644
--- a/Android.bp
+++ b/Android.bp
@@ -1,4 +1,5 @@
 subdirs = [
+    "apex",
     "binder",
     "build",
     "btif",