audio: Add a delay for DSP firmware loading

This is turned off by default.

Change-Id: Idf764933c67e6666cb2cc0043fa7a7e86935488d
diff --git a/audio/audio_hw.h b/audio/audio_hw.h
index fddeffc..da5cd86 100644
--- a/audio/audio_hw.h
+++ b/audio/audio_hw.h
@@ -355,6 +355,7 @@
     int                 card;
     struct mixer*       mixer;
     struct audio_route* audio_route;
+    struct timespec     dsp_poweroff_time;
 };
 
 struct audio_usecase {