Add screen state parameter

Change-Id: Iead23e0d91dac34d40e9e55f525916b73c31bcb5
diff --git a/include/hardware/audio.h b/include/hardware/audio.h
index 9bd62aa..01d79b2 100644
--- a/include/hardware/audio.h
+++ b/include/hardware/audio.h
@@ -91,6 +91,9 @@
 /* A2DP sink address set by framework */
 #define AUDIO_PARAMETER_A2DP_SINK_ADDRESS "a2dp_sink_address"
 
+/* Screen state */
+#define AUDIO_PARAMETER_KEY_SCREEN_STATE "screen_state"
+
 /**
  *  audio stream parameters
  */