Log Message:
Add a minimal implementation of the read_rom method for NetBSD, just
good enough to get newer xorg servers running.
(I need to double-check the PCI spec, but it is well possible that we
can't do much better anyway: ISTR the PCI spec allows devices to share
decoding ressources between ROM and runtime logics, which means there
is no safe way to read the original ROM at runtime. Correct me if
I'm wrong.)