irqchip: atmel-aic: Move binding doc to interrupt-controller directory

Move atmel aic driver doc to the interrupt-controller directory as the new
driver now lays in drivers/irqchip/atmel-aic.c.
Signed-off-by: Boris BREZILLON <boris.brezillon@free-electrons.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Link: https://lkml.kernel.org/r/1405012462-766-3-git-send-email-boris.brezillon@free-electrons.comSigned-off-by: Jason Cooper <jason@lakedaemon.net>