[VictoriaFalls] Add a VFS yunq stub and register it.

sys/victoriafalls/victoriafalls_server.cpp

@@ -0,0 +1,14 @@
+#include "victoriafalls_server.h"
+
+#include <zcall.h>
+
+glcr::ErrorOr<glcr::UniquePtr<VFSServer>> VFSServer::Create() {
+  z_cap_t endpoint_cap;
+  RET_ERR(ZEndpointCreate(&endpoint_cap));
+  return glcr::UniquePtr<VFSServer>(new VFSServer(endpoint_cap));
+}
+
+glcr::ErrorCode VFSServer::HandleOpenFile(const OpenFileRequest&,
+                                          OpenFileResponse&) {
+  return glcr::OK;
+}