Set apex_available for okhttp

We are making apex_available required to be set to
put modules into an apex.

Bug: 147364041
Test: m
Change-Id: I74dbd9a2b2a4bfb8b02252abec5cda649b80e43c
diff --git a/Android.bp b/Android.bp
index ee7ff2f..775ee88 100644
--- a/Android.bp
+++ b/Android.bp
@@ -81,6 +81,10 @@
         "conscrypt.module.intra.core.api.stubs",
     ],
     java_version: "1.7",
+    apex_available: [
+        "com.android.art.debug",
+        "com.android.art.release",
+    ],
 }
 
 // A guaranteed unstripped version of okhttp.