ARM: 9217/1: add definition of arch_irq_work_raise()

The arm <asm/irq_work.h> does not define arch_irq_work_raise()
so is triggering the following sparse warning. Add a definiton
to fix this:

kernel/irq_work.c:70:13: warning: symbol 'arch_irq_work_raise' was not declared. Should it be static?
arch/arm/kernel/smp.c:582:6: warning: symbol 'arch_irq_work_raise' was not declared. Should it be static?

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>