Don't map the full 16 MB PROM to prevent running out of kva.  We're only interested in the first few KB.
Don't map the full 16 MB PROM to prevent running out of kva.  We're only
interested in the first few KB.

ok grange@

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars