irqchip/bcm: Restore registration print with %pOF

It is useful to print which interrupt controllers are registered in the
system and which parent IRQ they use, especially given that L2 interrupt
controllers do not call request_irq() on their parent interrupt and do
not appear under /proc/interrupts for that reason.

We used to print the base register address virtual address which had
little value, use %pOF to print the path to the Device Tree node which
maps to the physical address more easily and is what people need to
troubleshoot systems.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>