Embedded has the DeviceTree standard to serve the same purpose as PCIe enumeration. This is even supported inside UEFI (which is how we will boot standard distros, once our kernel patches trickle upstream). There's no reason why not using PCIe means "creating all these piles of e-waste doomed to only run crappy outdated vendor kernels". What does that isn't whatever choice of device enumeration you use, it's vendors not bothering to upstream anything.
(This is another difference between the Asahi Linux project and Corellium's kernel; we're going through the bureaucracy of standardizing all of our DeviceTree bindings, which takes time but establishes a common reference that other OSes such as OpenBSD and bootloaders such as U-Boot can use to also support drivers for this hardware using our first-level bootloader.)
The canonical repo is the Linux kernel tree, so you go through there (and the DeviceTree maintainers). This is mostly for practical reasons since they are the primary consumer, but the bindings are packaged for use by other OSes too.
(This is another difference between the Asahi Linux project and Corellium's kernel; we're going through the bureaucracy of standardizing all of our DeviceTree bindings, which takes time but establishes a common reference that other OSes such as OpenBSD and bootloaders such as U-Boot can use to also support drivers for this hardware using our first-level bootloader.)