genirq: Introduce helper functions to support stacked irq_chip

Now we already support hierarchy irq_data, so introduce several helpers
to support stacked irq_chips.

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Grant Likely <grant.likely@linaro.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Yingjoe Chen <yingjoe.chen@mediatek.com>
Cc: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Git-commit: 85f08c17de26f117be6ca7aa260d2ec02a2248ba
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Puja Gupta <pujag@codeaurora.org>