virtio: Ensure PCI is set up first

Sometimes virtio may rely on PCI, or at least that is what the
distro_bootcmd script suggests. Add this in.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/virtio/virtio-uclass.c b/drivers/virtio/virtio-uclass.c
index b3fb3db..31bb21c 100644
--- a/drivers/virtio/virtio-uclass.c
+++ b/drivers/virtio/virtio-uclass.c
@@ -373,6 +373,12 @@
 {
 	int ret;
 
+	if (IS_ENABLED(CONFIG_PCI)) {
+		ret = uclass_probe_all(UCLASS_PCI);
+		if (ret && ret != -ENOENT)
+			return log_msg_ret("pci", ret);
+	}
+
 	ret = uclass_probe_all(UCLASS_VIRTIO);
 	if (ret && ret != -ENOENT)
 		return log_msg_ret("vir", ret);