virtio: cmd: Add virtio command for virtio devices

Add 'virtio' command in U-Boot command line.

Signed-off-by: Tuomas Tynkkynen <tuomas.tynkkynen@iki.fi>
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/Makefile b/cmd/Makefile
index ac4830a..12a1330 100644
--- a/cmd/Makefile
+++ b/cmd/Makefile
@@ -135,6 +135,7 @@
 obj-$(CONFIG_CMD_UBIFS) += ubifs.o
 obj-$(CONFIG_CMD_UNIVERSE) += universe.o
 obj-$(CONFIG_CMD_UNZIP) += unzip.o
+obj-$(CONFIG_CMD_VIRTIO) += virtio.o
 obj-$(CONFIG_CMD_LZMADEC) += lzmadec.o
 
 obj-$(CONFIG_CMD_USB) += usb.o disk.o