xen/arm: Fix deadlock in gic_set_guest_irq()

xen/arm: Fix deadlock in gic_set_guest_irq()

The possible deadlock scenario is explained below:

non interrupt context:    interrupt contex        interrupt context
                          (CPU0):                 (CPU1):
vgic_distr_mmio_write()   do_trap_irq()           do_softirq()
  |                         |                       |
  vgic_disable_irqs()       ...                     ...
    |                         |                       |
    gic_remove_from_queues()  vgic_vcpu_inject_irq()  vgic_vcpu_inject_irq()
    |  ...                      |                       |
    |  spin_lock(...)           gic_set_guest_irq()     gic_set_guest_irq()
    |  ...                        ...                     ...
    |  ... <----------------.---- spin_lock_irqsave(...)  ...
    |  ... <----------------.-.---------------------------spin_lock_irqsave(...)
    |  ...                  . .       Oops! The lock has already taken.
    |  spin_unlock(...)     . .
    |  ...                  . .
    gic_irq_disable()       . .
       ...                  . .
       spin_lock(...)       . .
       ...                  . .
       ... <----------------. .
       ... <------------------.
       ...
       spin_unlock(...)

Since the gic_remove_from_queues() and gic_irq_disable() called from
non interrupt context and they acquire the same lock as gic_set_guest_irq()
which called from interrupt context we must disable interrupts in these
functions to avoid possible deadlocks.

Change-Id: Ia354d87bb44418956e30cd7e49cc76616c359cc9
Signed-off-by: Oleksandr Tyshchenko <oleksandr.tyshchenko@globallogic.com>
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Julien Grall <julien.grall@linaro.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>