There are 3 interrupt groups each with its own status/mask registers.
We use a separate struct irq_chip for each interrupt group and handle
interrupts in two stages or levels: level 1 selects the appropriate
struct irq_chip, and level 2 selects individual interrupts within
that irq_chip.
Signed-off-by: NDale Farnsworth <dale@farnsworth.org>
Signed-off-by: NPaul Mackerras <paulus@samba.org>