man4: bring back ofw_console.4 and openfirm.4

Back when I wrote openfirm.4, sparc64 was the only architecture to
include the corresponding device. However, nowadays all supported
architectures will provied this Open Firmware interface, even x86
when built with FDT support.
As for ofw_console(4), powerpc actually was the first architecture
to ship it but we'll probably not see another consumer in future.

This partially reverts 702547720ca01437081fb1b6f9eb281c9541021b and
r357794 respectively, adjusting paths and content as appropriate.