irqchip: spear_shirq: Use proper irq chips for the different SoCs

Only spear300 has an actual mask register for the RAS interrupts. Add
an irq chip pointer to the shirq struct and initialize spear300 with
the actual implementation and the others with dummy_irq_chip. The
disabled RAS3 block has no irq chip assigned, so we can check for this
and remove the disabled member.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20140619212713.831341023@linutronix.de


Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>