irqchip/mips-gic: Add new DT property to reserve IPIs

The new property will allow to specify the range of GIC hwirqs to use for IPIs.

This is an optinal property. We preserve the previous behaviour of allocating
the last 2 * gic_vpes if it's not specified or DT is not supported.

Signed-off-by: Qais Yousef <qais.yousef@imgtec.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Ralf Baechle <ralf@linux-mips.org>
Cc: <jason@lakedaemon.net>
Cc: <marc.zyngier@arm.com>
Cc: <jiang.liu@linux.intel.com>
Cc: <linux-mips@linux-mips.org>
Cc: <lisa.parratt@imgtec.com>
Cc: Qais Yousef <qsyousef@gmail.com>
Link: http://lkml.kernel.org/r/1449580830-23652-20-git-send-email-qais.yousef@imgtec.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>