hw/alpha: Don't use get_system_io

Advancements in the ioport subsystem mean that we need no longer
thunk memory-mapped i/o through the system-io address space.

Signed-off-by: Richard Henderson <rth@twiddle.net>
hw/alpha: Don't machine check on missing pci i/o

Not really correct, but we don't implement all of the random devices
that the kernel looks for.  This is good enough to keep us booting.

Signed-off-by: Richard Henderson <rth@twiddle.net>
exec: Support 64-bit operations in address_space_rw

Honor the implementation maximum access size, and at least check
the minimum access size.

Signed-off-by: Richard Henderson <rth@twiddle.net>
hw/alpha: Drop latch_tmp hack

The memory and i/o core now support passing 64-bit accesses along
from the guest, so we no longer need to emulate them.

Signed-off-by: Richard Henderson <rth@twiddle.net>