Refactor audio thread to run both recording and playback.

Eliminates the pcmrec thread and keeps playback and recording engine
operation mutually-exclusive.

audio_thread.c contains the audio thread which branches to the
correct engine depending upon the request. It also handles the main
audio initialization.

Moves pcm_init into main.c just before dsp_init because I don't want
that one in audio_init in the new file.

(Also makes revision df6e1bc pointless ;)

Change-Id: Ifc1db24404e6d8dd9ac42d9f4dfbc207aa9a26e1

apps/recorder/recording.c

@@ -1074,10 +1074,6 @@ bool recording_screen(bool no_source)
 #endif
 
 #if CONFIG_CODEC == SWCODEC
-    /* This should be done before touching audio settings */
-    while (!pcm_is_initialized())
-       sleep(0);
-
     /* recording_menu gets messed up: so prevent manus talking */
     talk_disable(true);
     /* audio_init_recording stops anything playing when it takes the audio
@@ -1209,11 +1205,6 @@ bool recording_screen(bool no_source)
                 trig_width[i] = vp_top[i].width - pm_x[i];
             }
 
-#if CONFIG_CODEC == SWCODEC
-            audio_close_recording();
-            audio_init_recording();
-#endif
-
             rec_init_recording_options(&rec_options);
             rec_set_recording_options(&rec_options);