irqchip: gicv3-its: Fix unsafe locking reported by lockdep

irqchip: gicv3-its: Fix unsafe locking reported by lockdep

When compiled with CONFIG_LOCKDEP, the kernel shouts badly, saying
that my locking is unsafe. I'm afraid the kernel is right:

       CPU0                    CPU1
       ----                    ----
  lock(&its->lock);
                               local_irq_disable();
                               lock(&irq_desc_lock_class);
                               lock(&its->lock);
  <Interrupt>
    lock(&irq_desc_lock_class);

 *** DEADLOCK ***

The fix is to always take its->lock with interrupts disabled.

Reported-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Link: https://lkml.kernel.org/r/1425659870-11832-5-git-send-email-marc.zyngier@arm.com
Signed-off-by: Jason Cooper <jason@lakedaemon.net>