powerpc: "IRQ probe failed (0x0)" on powerbook

[Benjamin Herrenschmidt]

> Bisection has identified this patch:
> 
> commit f90bb153b1493719d18b4529a46ebfe43220ea6c
> Author: Benjamin Herrenschmidt <benh at kernel.crashing.org>
> Date:   Sat Nov 11 17:24:51 2006 +1100
> 
>     [POWERPC] Make pci_read_irq_line the default

Thanks Andreas ! I was expecting something around that patch indeed, I
suspect something in Apple device-tree is dodgy and breaking the
new generic PCI irq parsing (for example, at first sight, it's a PCI
device with 2 interrupts, which isn't allowed by the PCI spec).

I'll dig a bit more when I get to the office where my crash box is, and
will do a fix.

Ben.