[PATCH v1] riscv: make ZONE_DMA32 optional

[Vladimir Kondratiev]

>Well, this doesn't get any more true by just irgnoring the previous
>discussion and just reposting :(

Sorry, this wasn't the intention. Perhaps I messed with the message-id, I see my "patch v1" in one mail thread together with the previous discussion, but not in the other thread.

Anyway, I think making ZONE_DMA32 selection depend on NONPORTABLE answers the concern
that was raised