audio: Add audio parameter key for device connect

Add audio parameter key for device connect.

Bug: 17785277
Bug: 19214836
Change-Id: Icd81702634e0bd83645d89c2d65e2b303fc11f8c
(cherry picked from commit 55c07c3418a3bc19a72c4935d8ed57a57074c49a)
diff --git a/include/hardware/audio.h b/include/hardware/audio.h
index 8d5b2f0..2389c09 100644
--- a/include/hardware/audio.h
+++ b/include/hardware/audio.h
@@ -128,6 +128,7 @@
 #define AUDIO_PARAMETER_STREAM_INPUT_SOURCE "input_source"   /* audio_source_t */
 #define AUDIO_PARAMETER_STREAM_SAMPLING_RATE "sampling_rate" /* uint32_t */
 
+#define AUDIO_PARAMETER_DEVICE_CONNECT "connect"            /* audio_devices_t */
 #define AUDIO_PARAMETER_DEVICE_DISCONNECT "disconnect"      /* audio_devices_t */
 
 /* Query supported formats. The response is a '|' separated list of strings from