genirq: generic chip: Export irq_map_generic_chip function

Export the generic irq map function in order to provide irq_domain ops with
generic mapping and specific of xlate function (needed by the new atmel
AIC driver).

Signed-off-by: Boris BREZILLON <boris.brezillon@free-electrons.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/1405012462-766-2-git-send-email-boris.brezillon@free-electrons.com


Signed-off-by: Jason Cooper <jason@lakedaemon.net>