audio: sndmonitor

Monitor sound card status and report online/offline
events back to the streams registered with it and to audio_dev.

Bug: 30075678
CRs-Fixed: 1053073
Change-Id: Iea74d5c83f7fe92ba4a24f4f4650ce255bdb48e8
diff --git a/hal/platform_api.h b/hal/platform_api.h
index 625f4eb..ec64206 100644
--- a/hal/platform_api.h
+++ b/hal/platform_api.h
@@ -37,6 +37,8 @@
     int na_mode;
 } native_audio_prop;
 
+enum card_status_t;
+
 void *platform_init(struct audio_device *adev);
 void platform_deinit(void *platform);
 const char *platform_get_snd_device_name(snd_device_t snd_device);