platform/conf: accept CLCs in conf.Unknown()
platform/conf: accept CLCs in conf.Unknown()

It's only used in two user-facing applications, "kola spawn" and
"ore packet create-device". In both cases it would be convenient to
accept Container Linux Configs.

dm0-/mantle,dm0-/mantle,glevand/coreos--mantle,glevand/coreos--mantle