Use different scopes on the output bus depending on AudioUnit type

[Pehrsons]

As the inline comment says it seems a HAL unit for a device with >2 output channels reports only 2 channels on the input scope of the output bus. Not sure what these 2 reflect but let's differentiate VPIO (where input scope reports 1 which we want, and output scope reflects hw) and HAL units when selecting scope as they're the only types we use.

[ChunMinChang]

Thanks for the change!

Are there other coming commits? Landing this individually may cause a noise issue.

With this patch, the mNumberChannels of the given AudioBuffer provided by audiounit_output_callback will be matched to the channel count of the device, since now the output_dev_desc.mChannelsPerFrame matches output_hw_desc.mChannelsPerFrame's value.

However, if the channel count mismatches the output_stream_params.channels() channel, no mixer will be set up, and there will not be enough or too much data for the output buffer in the callback since the buffer (prepared by resampler) is for the output_stream_params.channels() channel.

I tested this with my Cubilux Surround Sound Card (CA7) with test_tone. Noise appears in all the channels.

[Pehrsons]

The new commit updates output_dev_desc so we configure the device correctly for 2 channels when deciding to skip the mixer. With my Studio Display that has 8 channels I get an error with the stereo variant of test_tone though:
AudioConverter.cpp:748 Failed to created a new in process converter -> from 2 ch, 48000 Hz, lpcm (0x00000009) 32-bit little-endian float, packed in 16 bytes low-aligned to 8 ch, 48000 Hz, Float32, interleaved, with status 1718449215
Note 1718449215 is the fourcc for fmt?, i.e. kAudioConverterErr_FormatNotSupported.

[Pehrsons]

Ah my bug, fixed now. With this stack playing something >2ch should work on a device with >2ch.

[ChunMinChang]

LGTM! thanks!