Document (overlapping) codenames for toolchains, platforms, Kconfigurations, signing schemes, etc.

[marc-hb]

What do "TGL" or "CHT" mean? Are they Intel SoCs, PCH codenames, Kconfigurations, toolchain names, signing schemes? Probably a bit of everything depending on the context, no one knows for sure. No one except @jajanusz , who agreed in #3451 (comment) that some documentation is really needed. Quoting myself from there:

I can think of two places: either sof-docs or the top of src/arch/extensa/CMakeLists.txt but maybe there is a better place.

[lgirdwood]

@marc-hb there is a platform description table in sof-docs - this info could be added in new columns. They are product names but also used for fw and toolchain config.

[marc-hb]

They are product names but also used for fw and toolchain config.

These "accidental" 1:1:1 mappings seem pretty bad. Because they "accidentally" work until they don't:
#3451 (comment)

Short of renaming everything to tgl-toolchain, tgl-kconfig, etc., some documentation would really help mitigate.

[marc-hb]

Thanks to thesofproject/sof-test#428 for this useful "bookmark": https://github.com/thesofproject/linux/blob/topic/sof-dev/sound/soc/sof/sof-pci-dev.c