random: add a Virtio RNG module

* The default module is replaced by the Virtio RNG module when found.
* This can have the undesired effect of rendering /dev/urandom slow.
* Tested with the following QEmu command line option:
-device virtio-rng-pci,rng=rng0 -object rng-random,filename=/dev/random,id=rng0
* moved random.h to private/drivers headers.

headers/private/drivers/random.h

@@ -0,0 +1,31 @@
+/*
+ * Copyright 2013, Haiku, Inc. All Rights Reserved.
+ * Distributed under the terms of the MIT License.
+ *
+ * Authors:
+ *		Jérôme Duval, [email protected]
+ */
+#ifndef _RANDOM_H
+#define _RANDOM_H
+
+
+#include <device_manager.h>
+
+
+typedef struct {
+	driver_module_info info;
+} random_for_controller_interface;
+
+
+#define RANDOM_FOR_CONTROLLER_MODULE_NAME "bus_managers/random/controller/driver_v1"
+
+// Bus manager interface used by Random controller drivers.
+typedef struct random_module_info {
+	driver_module_info info;
+
+	status_t (*read)(void* cookie, void *_buffer, size_t *_numBytes);
+	status_t (*write)(void* cookie, const void *_buffer, size_t *_numBytes);
+} random_module_info;
+
+
+#endif /* _RANDOM_H */