Move load_firmware() to separate file

The idea is to share loading code between bootloaders and rolo().

Change-Id: I1656ed91946d7a05cb7c9fa7a16793c3c862a5cd
Reviewed-on: http://gerrit.rockbox.org/190
Reviewed-by: Marcin Bukat <marcin.bukat@gmail.com>

firmware/include/rb-loader.h

@@ -0,0 +1,22 @@
+/***************************************************************************
+ *             __________               __   ___.
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ *
+ * Copyright (C) 2005 by Linus Nielsen Feltzing
+ *
+ * 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 1
+ * 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.
+ *
+ ****************************************************************************/
+
+const char *rb_strerror(int8_t errno);
+int load_firmware(unsigned char* buf, const char* firmware, int buffer_size);