mkosi: hook up i386 gpt pt types
mkosi: hook up i386 gpt pt types

Let's actually hook up the i386 gpt pt types to be used.

(This uses the list of known uname machine fields we use in systemd:
https://github.com/systemd/systemd/blob/main/src/basic/architecture.c#L32
)

systemd/mkosi,systemd/mkosi