doc: describe QEMU virtio block device

Enhance the description of QEMU block devices

* Describe how to attach a virtio-blk device.
* Sort the command lines for MMC to match the other devices.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/board/emulation/blkdev.rst b/doc/board/emulation/blkdev.rst
index dc83a00..f187ff2 100644
--- a/doc/board/emulation/blkdev.rst
+++ b/doc/board/emulation/blkdev.rst
@@ -11,8 +11,8 @@
   .. code-block:: bash
 
       -device sdhci-pci,sd-spec-version=3 \
-      -device sd-card,drive=MMC1 \
-      -drive if=none,file=disk.img,format=raw,id=MMC1
+      -drive if=none,file=disk.img,format=raw,id=MMC1 \
+      -device sd-card,drive=MMC1
 
 * NVMe
 
@@ -36,3 +36,13 @@
       -device qemu-xhci \
       -drive if=none,file=disk.img,format=raw,id=USB1 \
       -device usb-storage,drive=USB1
+
+* Virtio
+
+  .. code-block:: bash
+
+      -drive if=none,file=disk.img,format=raw,id=VIRTIO1 \
+      -device virtio-blk,drive=VIRTIO1
+
+  .. note::
+     As of v2023.07 U-Boot does not have a driver for virtio-scsi-pci.