virtio: rng: Add a random number generator(rng) driver

Add a driver for the virtio-rng device on the qemu platform. The
device uses pci as a transport medium. The driver can be enabled with
the following configs

CONFIG_VIRTIO
CONFIG_DM_RNG
CONFIG_VIRTIO_PCI
CONFIG_VIRTIO_RNG

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
index a9d5fd0..2e3dd3b 100644
--- a/drivers/virtio/Kconfig
+++ b/drivers/virtio/Kconfig
@@ -59,4 +59,10 @@
 	  This is the virtual block driver for virtio. It can be used with
 	  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.
 endmenu