bluetooth: Modular API for A2DP codecs

This patch introduce new modular API for bluetooth A2DP codecs. Its
benefits are:

* bluez5-util and module-bluez5-device does not contain any codec specific
  code, they are codec independent.

* For adding new A2DP codec it is needed just to adjust one table in
  a2dp-codec-util.c file. All codec specific functions are in separate
  codec file.

* Support for backchannel (microphone voice). Some A2DP codecs (like
  FastStream or aptX Low Latency) are bi-directional and can be used for
  both music playback and audio call.

* Support for more configurations per codec. This allows to implement low
  quality mode of some codec together with high quality.

Current SBC codec implementation was moved from bluez5-util and
module-bluez5-device to its own file and converted to this new A2DP API.

src/modules/bluetooth/a2dp-codec-util.c

@@ -0,0 +1,56 @@
+/***
+  This file is part of PulseAudio.
+
+  Copyright 2019 Pali Rohár <pali.rohar@gmail.com>
+
+  PulseAudio is free software; you can redistribute it and/or modify
+  it under the terms of the GNU Lesser General Public License as
+  published by the Free Software Foundation; either version 2.1 of the
+  License, or (at your option) any later version.
+
+  PulseAudio 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 Lesser General Public
+  License along with PulseAudio; if not, see <http://www.gnu.org/licenses/>.
+***/
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <pulsecore/core.h>
+#include <pulsecore/core-util.h>
+
+#include "a2dp-codec-util.h"
+
+extern const pa_a2dp_codec pa_a2dp_codec_sbc;
+
+/* This is list of supported codecs. Their order is important.
+ * Codec with higher index has higher priority. */
+const pa_a2dp_codec *pa_a2dp_codecs[] = {
+    &pa_a2dp_codec_sbc,
+};
+
+unsigned int pa_bluetooth_a2dp_codec_count(void) {
+    return PA_ELEMENTSOF(pa_a2dp_codecs);
+}
+
+const pa_a2dp_codec *pa_bluetooth_a2dp_codec_iter(unsigned int i) {
+    pa_assert(i < pa_bluetooth_a2dp_codec_count());
+    return pa_a2dp_codecs[i];
+}
+
+const pa_a2dp_codec *pa_bluetooth_get_a2dp_codec(const char *name) {
+    unsigned int i;
+    unsigned int count = pa_bluetooth_a2dp_codec_count();
+
+    for (i = 0; i < count; i++) {
+        if (pa_streq(pa_a2dp_codecs[i]->name, name))
+            return pa_a2dp_codecs[i];
+    }
+
+    return NULL;
+}