extract reset keyboard into a function

that makes it easy to call reset_keyboard() from a function in a keymap

quantum/quantum.h

@@ -77,6 +77,8 @@ bool process_action_kb(keyrecord_t *record);
 bool process_record_kb(uint16_t keycode, keyrecord_t *record);
 bool process_record_user(uint16_t keycode, keyrecord_t *record);
 
+void reset_keyboard(void);
+
 void startup_user(void);
 void shutdown_user(void);