hal: add support for hfp on auto platform

Add auto platform specific pcm device id and
playback volume control to support hfp with
dual asm loopback.

Change-Id: I6bd2ae63c8733dd770f48c1b2557c4d3d5a6b101
diff --git a/hal/audio_extn/hfp.c b/hal/audio_extn/hfp.c
index b0c14cd..95f463d 100644
--- a/hal/audio_extn/hfp.c
+++ b/hal/audio_extn/hfp.c
@@ -55,6 +55,8 @@
 #define HFP_RX_VOLUME     "SEC AUXPCM LOOPBACK Volume"
 #elif defined PLATFORM_MSM8996
 #define HFP_RX_VOLUME     "PRI AUXPCM LOOPBACK Volume"
+#elif defined PLATFORM_AUTO
+#define HFP_RX_VOLUME     "Playback 36 Volume"
 #elif defined (PLATFORM_MSM8998) || defined (PLATFORM_MSMFALCON) || defined (PLATFORM_SDM845) || defined (PLATFORM_SDM710) || defined (PLATFORM_QCS605) || defined (PLATFORM_MSMNILE) || defined (PLATFORM_MSMSTEPPE) || defined (PLATFORM_QCS405)
 #define HFP_RX_VOLUME     "SLIMBUS_7 LOOPBACK Volume"
 #else