sandbox: Tidy up terminal restore

For some reason 'u-boot -D' does not restore the terminal correctly when
the 'reset' command is used. Call the terminal restore function explicitly
in this case.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>

include/os.h

@@ -111,6 +111,14 @@ void os_exit(int exit_code) __attribute__((noreturn));
  */
 void os_tty_raw(int fd, bool allow_sigs);
 
+/**
+ * Restore the tty to its original mode
+ *
+ * Call this to restore the original terminal mode, after it has been changed
+ * by os_tty_raw(). This is an internal function.
+ */
+void os_fd_restore(void);
+
 /**
  * Acquires some memory from the underlying os.
  *