qemu-arm: Enable VirtIO distro target

With -device virtio-blk-device,drive=hd0, it could detect distro boot
target.
Signed-off-by: NSumit Garg <sumit.garg@linaro.org>
Reviewed-by: NAlexander Graf <agraf@suse.de>

include/configs/qemu-arm.h

@@ -25,6 +25,7 @@
 
 #define BOOT_TARGET_DEVICES(func) \
 	func(SCSI, scsi, 0) \
+	func(VIRTIO, virtio, 0) \
 	func(DHCP, dhcp, na)
 
 #include <config_distro_bootcmd.h>