3ds: 3ds port sources. Second set of two.

This commit adds new files written exclusively for the 3ds port.

Additional comments:

1. Plugins works, but will be enabled in future commits.
2. The port has only been tested on the New 3DS.
3. Not all features of rockbox have been tested so there may be bugs or non-functional features.
4. There is a known issue where a random crash can occur when exiting the app.

Change-Id: I122d0bea9aa604e04fca45ba8287cf79e6110769

firmware/target/hosted/ctru/app/backlight-target.h

@@ -0,0 +1,32 @@
+/***************************************************************************
+ *             __________               __   ___
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ *
+ * Copyright (C) 2017 Marcin Bukat
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ****************************************************************************/
+
+#ifndef _BACKLIGHT_TARGET_H_
+#define _BACKLIGHT_TARGET_H_
+
+#include <stdbool.h>
+
+/* See backlight.c */
+bool backlight_hw_init(void);
+void backlight_hw_on(void);
+void backlight_hw_off(void);
+void backlight_hw_brightness(int brightness);
+
+#endif