When we're done with one interrupt, we need to search for the next pending
interrupt in the queue. This search has grown quite big now that we have
more than 256 possible irq lines.

So let's memorize how many interrupts we have pending in our bitmaps, so
that we can always bail out in the usual case - the one where we're all done.
Signed-off-by: NAlexander Graf <agraf@suse.de>