audio/hal: Configure HDMI channels based on output stream channels

- Current HAL configures HDMI channels based on sink capabilities,
  even when the output content is stereo. DSP upmixes the content
  if the HDMI backend is configured for 5.1 channels.
- This change ensures that HDMI backend is configured based on
  output stream channels.

Bug: 7290997.
Change-Id: I42b2773b8f4ccc62203c13ff9ac6a6511df0705f
diff --git a/hal/audio_hw.h b/hal/audio_hw.h
index 717c0a6..0da4324 100644
--- a/hal/audio_hw.h
+++ b/hal/audio_hw.h
@@ -39,6 +39,7 @@
 #define ACDB_DEV_TYPE_IN 2
 
 #define MAX_SUPPORTED_CHANNEL_MASKS 2
+#define DEFAULT_HDMI_OUT_CHANNELS   2
 
 typedef int snd_device_t;
 
@@ -188,6 +189,7 @@
     struct audio_route *audio_route;
     int acdb_settings;
     bool speaker_lr_swap;
+    unsigned int cur_hdmi_channels;
 
     void *platform;