The recent changes for ioport memory regions is a blessing and a
curse for the simplified alpha machine model we have.
On the one hand, we can eliminate two hacks present in the tsunami
system chip emulation. We also now get machine checks when we access
ioports that aren't connected to a device.
On the other hand, we aren't currently connecting many of the silly
little isa devices normally handled by the SuperIO chip hanging off
the PCI bus. Stuff we don't really need for the running kernel, but
gets initialized during normal startup anyway. E.g. the ISA DMA
engine and the com2 uart.
The later device is particularly annoying, since we can't actually
get to qemu_chr_open_null at the moment. Rather than properly fill
in the blanks, I cheat in the second patch and just discard unused
reads and writes in the isa io region. This restores the state of
affairs we had before the recent changes.