tools/virtio: add dev_WARN_ONCE and is_vmalloc_addr stubs

Add dev_WARN_ONCE and is_vmalloc_addr stubs needed by virtio_ring.c.
is_vmalloc_addr stub always returns false - that's fine since it's
merely a sanity check.

Created using Cursor CLI.

Message-ID: <749e7a03b7cd56baf50a27efc3b05e50cf8f36b6.1764873799.git.mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>