audio flinger: pass mixer configuration when opening an audio output

Add the possibility for audio policy manager to indicate a mixer
audio configuration (channel mask, format, sampling rate)
different from the audio HAL stream configuration when opening an
output stream with IAudioflinger::openOutput().

Bug: 188502620
Test: atest audiopolicy_tests

Change-Id: I0b4eaa9cd3e5574b75e3b914c854f97c104ca07e
diff --git a/services/audiopolicy/tests/AudioPolicyManagerTestClient.h b/services/audiopolicy/tests/AudioPolicyManagerTestClient.h
index f7b0565..84b40d2 100644
--- a/services/audiopolicy/tests/AudioPolicyManagerTestClient.h
+++ b/services/audiopolicy/tests/AudioPolicyManagerTestClient.h
@@ -37,7 +37,8 @@
 
     status_t openOutput(audio_module_handle_t module,
                         audio_io_handle_t *output,
-                        audio_config_t * /*config*/,
+                        audio_config_t * /*halConfig*/,
+                        audio_config_base_t * /*mixerConfig*/,
                         const sp<DeviceDescriptorBase>& /*device*/,
                         uint32_t * /*latencyMs*/,
                         audio_output_flags_t /*flags*/) override {