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/luminance-ctru.h

@@ -0,0 +1,40 @@
+/*
+*   This file is part of Luma3DS
+*   Copyright (C) 2016-2020 Aurora Wright, TuxSH
+*
+*   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 3 of the License, or
+*   (at your option) any later version.
+*
+*   This program is distributed in the hope that it will be useful,
+*   but WITHOUT ANY WARRANTY; without even the implied warranty of
+*   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+*   GNU General Public License for more details.
+*
+*   You should have received a copy of the GNU General Public License
+*   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*
+*   Additional Terms 7.b and 7.c of GPLv3 apply to this file:
+*       * Requiring preservation of specified reasonable legal notices or
+*         author attributions in that material or in the Appropriate Legal
+*         Notices displayed by works containing it.
+*       * Prohibiting misrepresentation of the origin of that material,
+*         or requiring that modified versions of such material be marked in
+*         reasonable ways as different from the original version.
+*/
+
+#ifndef _LUMINANCE_CTRU_H_
+#define _LUMINANCE_CTRU_H_
+
+#include <3ds/types.h>
+
+extern u32 ctru_min_lum;
+extern u32 ctru_max_lum;
+extern u32 ctru_luminance;
+
+u32 getMinLuminancePreset(void);
+u32 getMaxLuminancePreset(void);
+u32 getCurrentLuminance(bool top);
+
+#endif /*  _LUMINANCE_CTRU_H_ */