hal: Add device sidetone support for USB audio ADSP solution

Add device sidetone support for USB ADSP solution if the USB headset
has the sidetone capability.

CRs-Fixed: 1019158
Change-Id: Ie40c286eb9988aeb5093f32c7f81cdb142e88eb6
diff --git a/hal/platform_api.h b/hal/platform_api.h
index cb177b6..c6f3cb3 100644
--- a/hal/platform_api.h
+++ b/hal/platform_api.h
@@ -148,4 +148,8 @@
                                    snd_device_t *new_snd_devices);
 
 bool platform_check_backends_match(snd_device_t snd_device1, snd_device_t snd_device2);
+int platform_set_sidetone(struct audio_device *adev,
+                          snd_device_t out_snd_device,
+                          bool enable,
+                          char * str);
 #endif // AUDIO_PLATFORM_API_H