deterministic ALSA names for duplicate audio devices

[markferry]

When a zone uses more than one USB audio device (same make, model, etc) device names (like Device, Device_1) are non-deterministic on boot.

Make static assignments for the devices so they're always in the same order.

[markferry]

This arose because I wanted to use audio passthrough. With vc4-fkms-v3d driver.
Switching to the vc4-kms-driver provides working passthrough but then software mixing isn't possible (#20).

One solution is to use kms then split the Kodi and Snapclient streams to separate audio devices. It means having to switch inputs on the AV receiver. (With AV receiver network protocol or perhaps HDMI-CEC)

Adding a second identical USB audio device means it's random which of the two gets which name.

[markferry]

diff -u <(udevadm info -q all -a -p /sys/class/sound/card0) <(udevadm info -q all -a -p /sys/class/sound/card2) | less

[markferry]

https://stackoverflow.com/a/44218856

/etc/udev/rules.d/70-my-sound-cards.rules