Initial opus codec support

Synchronised with opus repo on github (https://github.com/freqmod/rockbox-opus)

Status:
* Seeking ported from speex, but fails on some cases (e.g. seek to granule 0)
* ReplayGain parsing needs to be reworked, we do vorbis-style replaygain now.
  http://wiki.xiph.org/OggOpus#Comment_Header explicitly forbids these in
  favour of R128_TRACK_GAIN tag.
* No optimisation yet, source files still nearly identical to opus upstream
* Multi-stream opus files may not be parsed correctly

Change-Id: Ia66f1027dc1d288083e3c57b2816700078376f9a
Reviewed-on: http://gerrit.rockbox.org/300
Reviewed-by: Bertrik Sikken <bertrik@sikken.nl>
Tested-by: Bertrik Sikken <bertrik@sikken.nl>

lib/rbcodec/codecs/libopus/opus_config.h

@@ -0,0 +1,42 @@
+#ifndef CONFIG_H
+#define CONFIG_H
+
+#include "config.h"
+#include "codeclib.h"
+
+/* general stuff */
+#define OPUS_BUILD
+
+/* alloc stuff */
+#define NONTHREADSAFE_PSEUDOSTACK
+
+#define OVERRIDE_OPUS_ALLOC
+#define OVERRIDE_OPUS_FREE
+#define OVERRIDE_OPUS_ALLOC_SCRATCH
+
+#define opus_alloc          codec_malloc
+#define opus_free           codec_free
+#define opus_alloc_scratch  codec_malloc
+
+/* lrint */
+#define HAVE_LRINTF 0
+#define HAVE_LRINT  0
+
+/* embedded stuff */
+#define FIXED_POINT
+#define DISABLE_FLOAT_API
+#define EMBEDDED_ARM 1
+
+/* undefinitions */
+#ifdef ABS
+#undef ABS
+#endif
+#ifdef MIN
+#undef MIN
+#endif
+#ifdef MAX
+#undef MAX
+#endif
+
+#endif /* CONFIG_H */
+