z8530_interrupt -- Handle an interrupt from a Z8530
(int irq, void * dev_id, struct pt_regs * regs);
The Z8530 device that is interrupting.
A Z8530 device has stuck its hand in the air for attention.
We scan both the channels on the chip for events and then call
the channel specific call backs for each channel that has events.
We have to use callback functions because the two channels can be
in different modes.