genirq: Add new IPI irqdomain flags

genirq: Add new IPI irqdomain flags

These flags will be used to identify an IPI domain. We have two flavours of
IPI implementations:

IRQ_DOMAIN_FLAG_IPI_PER_CPU: Each CPU has its own virq and hwirq
IRQ_DOMAIN_FLAG_IPI_SINGLE : A single virq and hwirq for all CPUs

Signed-off-by: Qais Yousef <qais.yousef@imgtec.com>
Cc: <jason@lakedaemon.net>
Cc: <marc.zyngier@arm.com>
Cc: <jiang.liu@linux.intel.com>
Cc: <ralf@linux-mips.org>
Cc: <linux-mips@linux-mips.org>
Cc: <lisa.parratt@imgtec.com>
Cc: Qais Yousef <qsyousef@gmail.com>
Link: http://lkml.kernel.org/r/1449580830-23652-2-git-send-email-qais.yousef@imgtec.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>