sam460ex: Fix PCI interrupts with multiple devices

The four interrupts of the PCI bus are connected to the same UIC pin
on the real Sam460ex. Evidence for this can be found in the UBoot
source for the Sam460ex in the Sam460ex.c file where
PCI_INTERRUPT_LINE is written. Change the ppc440_pcix model to behave
more like this.

This fixes the problem that can be observed when adding further PCI
cards that got their interrupt rotated to other interrupts than PCI
INT A. In particular, the bug was observed with an additional OHCI PCI
card or an ES1370 sound device.

Signed-off-by: Sebastian Bauer <mail@sebastianbauer.info>
Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Tested-by: Sebastian Bauer <mail@sebastianbauer.info>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>