AT91: Convert to fasteoi IRQ handler, and remove ARM irq_finish

[Andrew Victor]

hi Sebastian,

>>> why does this handler mess with the parent irq chip ?
>>> this looks pretty wrong to me.
>>
>>This is a chained-handler, and without that line the end-of-interrupt
>>doesn't seem to be signalled.
>
> Most chain handler don't mess with other irq chips. Why is the parent
> irq hanlder set level and not eoi? Wouldn't this make this superflous?

This patch changes the parent from level to eoi.