The IRQ Route Control registers definitions belong to the PIIX
chipset. We were only defining the 'A' register. Define the other
B, C and D registers, and use them.
Acked-by: Paul Durrant <paul@xen.org>
Reviewed-by: Aleksandar Markovic <amarkovic@wavecomp.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>