virtio: VIRTIO_RNG depends on DM_RNG

Add the missing Kconfig dependency and let VIRTIO_RNG default to yes.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
index 2e3dd3b..e800720 100644
--- a/drivers/virtio/Kconfig
+++ b/drivers/virtio/Kconfig
@@ -60,9 +60,11 @@
 	  QEMU based targets.
 
 config VIRTIO_RNG
-       bool "virtio rng driver"
-       depends on VIRTIO
-       help
-         This is the virtual random number generator driver. It can be used
-	 with Qemu based targets.
+	bool "virtio rng driver"
+	depends on DM_RNG
+	depends on VIRTIO
+	default y
+	help
+	  This is the virtual random number generator driver. It can be used
+	  with QEMU based targets.
 endmenu