Add set_irq_wake() support to intc using sysdev and suspend.

The intc controllers are put on a list at registration time
and registered as sysdev devices later on during the boot.

The sysdev class suspend callback is used to find irqs with
wakeup enabled belonging to our intc controller. Such irqs
are simply enabled so wakeup interrupts may reach the cpu.
Signed-off-by: NMagnus Damm <damm@igel.co.jp>
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>