ARM: 8367/1: sa1100: prepare for moving irq driver to drivers/irqchip

Prepare for moving sa1100 irq driver to irqchip infrastructure - split
sa1100_init_irq into helper code and irq parts.

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>