Implement HAL API get_presentation_position

This does _not_ address bug 10551158 (to include DSP buffering)

Change-Id: Ifbc5ca21c46eced3f93a891200c763a062625dd9
diff --git a/hal/audio_hw.h b/hal/audio_hw.h
index b61bcd4..03f276f 100644
--- a/hal/audio_hw.h
+++ b/hal/audio_hw.h
@@ -109,6 +109,7 @@
     /* Array of supported channel mask configurations. +1 so that the last entry is always 0 */
     audio_channel_mask_t supported_channel_masks[MAX_SUPPORTED_CHANNEL_MASKS + 1];
     bool muted;
+    uint64_t written; /* total frames written, not cleared when entering standby */
 
     int non_blocking;
     int playback_started;