irqchip: gic: Support hierarchy irq domain.

Add support to use gic as a parent for stacked irq domain.

Signed-off-by: Yingjoe Chen <yingjoe.chen@mediatek.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Link: https://lkml.kernel.org/r/1416902662-19281-2-git-send-email-yingjoe.chen@mediatek.com
Signed-off-by: Jason Cooper <jason@lakedaemon.net>
diff --git a/drivers/irqchip/Kconfig b/drivers/irqchip/Kconfig
index aaa260b..d47fa84 100644
--- a/drivers/irqchip/Kconfig
+++ b/drivers/irqchip/Kconfig
@@ -5,6 +5,7 @@
 config ARM_GIC
 	bool
 	select IRQ_DOMAIN
+	select IRQ_DOMAIN_HIERARCHY
 	select MULTI_IRQ_HANDLER
 
 config GIC_NON_BANKED