hal: add new proxy usecase for hearding aid

Add a dedicated proxy usecase for hearing aid.

Change-Id: Iacc828f23393e3b44e9eefed89bbb365240a9813
diff --git a/hal/msm8974/platform.h b/hal/msm8974/platform.h
index be138c0..6b2a671 100644
--- a/hal/msm8974/platform.h
+++ b/hal/msm8974/platform.h
@@ -612,6 +612,7 @@
 
 #define AFE_PROXY_PLAYBACK_PCM_DEVICE 7
 #define AFE_PROXY_RECORD_PCM_DEVICE 8
+#define AFE_PROXY_RECORD2_PCM_DEVICE 40
 
 #ifdef PLATFORM_MSM8x26
 #ifdef EXTERNAL_BT_SUPPORTED