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: Idd7706a931fde0dfd77fe8b58f6f0c84081c6e3c
diff --git a/Android.bp b/Android.bp
index d398426..b512fc2 100644
--- a/Android.bp
+++ b/Android.bp
@@ -74,4 +74,8 @@
         "-Wno-sign-compare",
         "-Wno-tautological-compare",
     ],
+    apex_available: [
+        "//apex_available:platform",
+        "com.android.virt",
+    ],
 }