audio: Propagate fatal error during offload to AF

Use offload callback thread to propagate fatal error
back to AF. AF can take action (invalidating tracks,
putting stream to standby) accordingly

Bug: 30075678
Change-Id: I426d6a7ff2a49cca7864ebea2c6be500bdb751b9
diff --git a/hal/audio_hw.h b/hal/audio_hw.h
index 55c3be4..5ce3018 100644
--- a/hal/audio_hw.h
+++ b/hal/audio_hw.h
@@ -133,6 +133,7 @@
     OFFLOAD_CMD_DRAIN,              /* send a full drain request to DSP */
     OFFLOAD_CMD_PARTIAL_DRAIN,      /* send a partial drain request to DSP */
     OFFLOAD_CMD_WAIT_FOR_BUFFER,    /* wait for buffer released by DSP */
+    OFFLOAD_CMD_ERROR,              /* offload playback hit some error */
 };
 
 enum {