hal: add support for external FM volume control

APQ8084 uses an external chip for FM. Add support for
mixer control for external FM volume control.

Change-Id: I296d0b32fce632a296057e6d7b48698d9b0648fe
diff --git a/hal/msm8960/platform.h b/hal/msm8960/platform.h
index e38d801..e326785 100644
--- a/hal/msm8960/platform.h
+++ b/hal/msm8960/platform.h
@@ -118,4 +118,7 @@
 #define AUDIO_CAPTURE_PERIOD_DURATION_MSEC 20
 #define AUDIO_CAPTURE_PERIOD_COUNT 2
 
+/* Define macro for Internal FM volume mixer */
+#define FM_RX_VOLUME "Internal FM RX Volume"
+
 #endif // QCOM_AUDIO_PLATFORM_H