vmbase: Make vmbase_elf_defaults android_arm64-only

Prevent building ELF images for all targets when built directly.

Test: TH
Change-Id: I56468c1f0e53cfa224ff9db67f7fe98a05bcaec9
diff --git a/vmbase/Android.bp b/vmbase/Android.bp
index ab87053..35484ea 100644
--- a/vmbase/Android.bp
+++ b/vmbase/Android.bp
@@ -49,6 +49,12 @@
         "libarm-optimized-routines-mem",
         "libvmbase_entry",
     ],
+    enabled: false,
+    target: {
+        android_arm64: {
+            enabled: true,
+        },
+    },
 }
 
 rust_library_rlib {