stdio: Add force parameter to stdio_deregister

In some cases we really want to move forward with a deregister, add a force
parameter to allow this, and replace the dev with a nulldev in this case.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
diff --git a/include/stdio_dev.h b/include/stdio_dev.h
index 268de8e..24da23f 100644
--- a/include/stdio_dev.h
+++ b/include/stdio_dev.h
@@ -103,8 +103,8 @@
 
 void	stdio_print_current_devices(void);
 #ifdef CONFIG_SYS_STDIO_DEREGISTER
-int	stdio_deregister(const char *devname);
-int stdio_deregister_dev(struct stdio_dev *dev);
+int stdio_deregister(const char *devname, int force);
+int stdio_deregister_dev(struct stdio_dev *dev, int force);
 #endif
 struct list_head* stdio_get_list(void);
 struct stdio_dev* stdio_get_by_name(const char* name);