add crosvm to com.android.virt

To do so, crosvm and its dependencies have the apex_available property
set to "//apex_available:platform", "com.android.virt" to explicitly
acknowledge the joining.

Bug: 174639241
Test: m com.android.virt
Change-Id: I11f02fea20b81f070ce5fb245eebb70421bb4e0b
diff --git a/Android.bp b/Android.bp
index 9b3d5ff..458bcc9 100644
--- a/Android.bp
+++ b/Android.bp
@@ -107,6 +107,10 @@
             ],
         },
     },
+    apex_available: [
+        "//apex_available:platform",
+        "com.android.virt",
+    ],
 }
 
 cc_library_static {