genirq: Export enable/disable_percpu_irq()

These functions are used by the tilegx onchip network driver, and it's
useful to be able to load that driver as a module.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
Link: http://lkml.kernel.org/r/201302012043.r11KhNZF024371@farm-0021.internal.tilera.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>