Build: generate initrd images for the hypervisor.

This packages the VMs to create the initial RAM disk.

Change-Id: I31f1a0650583eb4122233beb0abaa933909cb389
diff --git a/BUILD.gn b/BUILD.gn
index 6d5dae0..4b21696 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -5,7 +5,7 @@
 
   deps = [
     ":hypervisor",
-    "//test/vm:test_vm($arch_toolchain)",
+    "//test/vm:test_vm_initrd($arch_toolchain)",
   ]
 }