dev: implement generic devices

generic devices don't have a type (char, block, etc) and are created
by bus drivers to represent the device until a suitable driver is found.

generic devices are registered by the bus driver. once a more suitable
driver is found, that driver will re-register the device under itself.

dev/input.c

@@ -24,6 +24,12 @@ struct input_device *input_device_create(void)
 	return INPUT_DEVICE(dev);
 }
 
+struct input_device *input_device_from_generic(struct device *dev)
+{
+	dev->dev_type = DEV_TYPE_INPUT;
+	return INPUT_DEVICE(dev);
+}
+
 kern_status_t input_device_report_event(struct input_device *dev, const struct input_event *ev, bool noblock)
 {
 	struct ringbuffer *event_queue = &dev->i_events;