Make the VM Payload API explicitly public

The .so and headers for the API should be usable by any VM payload, so
make sure they are visible.

Bug: 335311756
Test: Still builds
Change-Id: I8594f1b13248221583562e6a496d003de1a98be3
diff --git a/vm_payload/Android.bp b/vm_payload/Android.bp
index 97d4649..229f533 100644
--- a/vm_payload/Android.bp
+++ b/vm_payload/Android.bp
@@ -79,6 +79,7 @@
         // Implementation is available inside a Microdroid VM.
         implementation_installable: false,
     },
+    visibility: ["//visibility:public"],
 }
 
 // Just the headers. Mostly useful for clients that only want the
@@ -88,6 +89,7 @@
     defaults: ["avf_build_flags_cc"],
     apex_available: ["com.android.compos"],
     export_include_dirs: ["include"],
+    visibility: ["//visibility:public"],
 }
 
 // Restricted headers for use by internal clients & associated tests.