Not all channels of ThinkPad Yoga X1 speakers show up in pavucontrol

Summary

Lenovo ThinkPad Yoga X1 laptop has 4.1 channel audio, but only left and right stereo speakers show up in pavucontrol

environment

Steps to reproduce

Have a Lenovo ThinkPad Yoga X1 laptop and install openSUSE Tumbleweed with KDE Plasma 5.19 on it
Build PulseAudio 14 from source (git master)
Install sof-firmware package, per https://wiki.archlinux.org/index.php/Lenovo_ThinkPad_X1_Yoga_%28Gen_4%29
Open pavucontrol app and go to Output Devices tab
Click the lock button for the device corresponding to the speakers

What is the current bug behavior?

pavucontrol only shows "Front Left" and "Front Right" speakers. However this laptop has 4.1 channel audio, so there should be more than that listed there.

What is the expected correct behavior?

All of the channels of the audio device are listed.

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