provide stubs for enable_irq_wake() and disable_irq_wake()

Provide {enable,disable}_irq_wakeup dummies for undefined
cross-compilers for platforms without CONFIG_GENERIC_IRQ.

Needed by wake-up-from-a-serial-port.patch

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>