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/char.c

@@ -11,3 +11,9 @@ struct char_device *char_device_create(void)
 
 	return CHAR_DEVICE(dev);
 }
+
+struct char_device *char_device_from_generic(struct device *dev)
+{
+	dev->dev_type = DEV_TYPE_CHAR;
+	return CHAR_DEVICE(dev);
+}