handle_prio_irq is almost identical with handle_fasteoi_irq. The
subtle differences are

1) The handler checks for IRQ_DISABLED after the device handler has
   been called. In case it's set it masks the interrupt.

2) When the handler sees IRQ_DISABLED on entry it masks the interupt
   in the same way as handle_fastoei_irq, but does not set the
   IRQ_PENDING flag.

3) Instead of gracefully handling a recursive interrupt it crashes the
   kernel.

#1 is just relevant when a device handler calls disable_irq_nosync()
   and it does not matter whether we mask the interrupt right away or
   not. We handle lazy masking for disable_irq anyway, so there is no
   real reason to have this extra mask in place.

#2 will prevent the resend of a pending interrupt, which can result in
   lost interrupts for edge type interrupts. For level type interrupts
   the resend is a noop in the generic code. According to the
   datasheet all interrupts are level type, so marking them as such
   will result in the exact same behaviour as the private
   handle_prio_irq implementation.

#3 is just stupid. Crashing the kernel instead of handling a problem
   gracefully is just wrong. With the current semantics- all handlers
   run with interrupts disabled - this is even more wrong.

Rename ack to eoi, remove the unused mask_ack, switch to
handle_fasteoi_irq and remove the private function.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Acked-by: Uwe Kleine-Koenig <u.kleine-koenig@pengutronix.de>
Cc: linux-arm-kernel@lists.infradead.org
LKML-Reference: <20110202212552.299898447@linutronix.de>