ARM: footbridge: fix PCI interrupt mapping

Since commit 30fdfb92 ("PCI: Add a call to pci_assign_irq() in
pci_device_probe()"), the PCI code will call the IRQ mapping function
whenever a PCI driver is probed. If these are marked as __init, this
causes an oops if a PCI driver is loaded or bound after the kernel has
initialised.

Fixes: 30fdfb92

 ("PCI: Add a call to pci_assign_irq() in pci_device_probe()")
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>