[PATCH] Fix 8250 probe on ppc32

[Benjamin Herrenschmidt]

> How early on can we use udbg? I'd be interested to see how this is  
> going to work out for 4xx/83xx/85xx w/built-in 8250's.

As soon as you can get something mapped I suppose... On ppc32 with
BootX, I setup a BAT in head.S, thus udbg is available in
machine_init(). On ppc64 with hypervisor console, we can enable hacks
that initialize udbg in real mode.

Ben.