audio: Initial support for amplifier HALs

Change-Id: I04ef5b89ca595a0df02f6a4a68748bd0d0cdb245
(cherry picked from commit 7a82a0e691d884045c78d1cb9f7ab0dd51a5d871)
diff --git a/audio/audio_hw.h b/audio/audio_hw.h
index d05acde..f1de6e8 100644
--- a/audio/audio_hw.h
+++ b/audio/audio_hw.h
@@ -20,6 +20,7 @@
 
 #include <cutils/list.h>
 #include <hardware/audio.h>
+#include <hardware/audio_amplifier.h>
 
 #include <tinyalsa/asoundlib.h>
 #include <tinycompress/tinycompress.h>
@@ -428,6 +429,7 @@
     int                     (*sound_trigger_close_for_streaming)(int);
 
     pthread_mutex_t         lock_inputs; /* see note below on mutex acquisition order */
+    amplifier_device_t      *amp;
 };
 
 /*